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CODING (Encyclopedia of Animal Cognition and Behavior 1st Ed)
Abstract
The neural, behavioral, and cognitive processes that convert experiences into neural and cognitive representations of experiences in sensation, perception, conditioning, memory, anticipation, problem solving, language, and related cognitive systems.
... [17] The presence and evolution of sexual dimorphism result in distinct life histories between the sexes, enabling individuals to fulfill diverse roles in reproduction and survival. [18] Notably, despite significant progress sexual dimorphism research, exploration of the molecular mechanisms responsible for these observed differences has been limited. ...
Sexual dimorphism is a crucial aspect of mating and reproduction in many animals, yet the molecular mechanisms remain unclear. In Bactrocera dorsalis, sex pheromones trimethylpyrazine (TMP) and tetramethylpyrazine (TTMP) are specifically synthesized by Bacillus strains in the male rectum. In the female rectum, Bacillus strains are found, but TMP and TTMP are not, indicating sexually dimorphic differences in sex pheromone synthesis. Our anatomical observations and precursor measurements revealed significant differences in rectal structure and ammonium levels between sexes. In vitro and in vivo experiments reveal that ammonium is vital for sex pheromone synthesis in rectal Bacillus strains. Comparative transcriptome analysis identified ammonium‐producing genes (carboxypeptidase B and peptide transporter) in the protein digestion pathway that show much higher expression in the male rectum than in the female rectum. Knocking down the expression of either carboxypeptidase B (or inhibiting enzyme activity) or peptide transporter decreases rectal ammonium levels significantly, resulting in the failure of sex pheromone synthesis in the male rectum. This study provides insights into the presence of sexual dimorphism in internal organs and their functionalities in male‐specific sex pheromone synthesis and has significant implications for understanding the molecular mechanisms underlying sex pheromone synthesis by symbionts in insects.
... The value of fecundity is influenced by a number of issues like size, age, environmental conditions, stocking ration, and dietary constituents (Ganias, 2017;Helmizuryani et al., 2020;Tsadik & Bart, 2007). The present findings were differed from (Uddin et al., 2017) who reported that the absolute fecundity of Vietnamese koi, A. testudineus were 16,832-46,186 for 14-17 cm length and 66-89 g sized fish during his study period. ...
The present research work has been carried out to obtain evidence on breeding and embryonic growth of A. testudineus by using S-GnRHa. Fish were injected with three different doses (0.25, 0.5, and 1.0 mL/kg body weight) of synthetic hormone S-GnRHa each with three replications, where male brood fish received half of the doses of female. The fecundity of A. testudineus was ranged from 47,227 to 77,561 during the study period and except control group all the hormone received group ovulated within 12 hours of hormone injection. Among all groups, the highest fertilization rate (89.33%), highest hatching rate (79.5%) as well as highest survival rate (67.0%) was obtained at 0.5 mL/kg body weight hormone dose recipient group. The fertilized egg's diameter was recorded as 77.59 ± 3.50 µm. The first cleavage had appeared within 18-25 min of fertilization and eventually the morula, blastula, and gastrula stages were observed at 3:10 h, 4 h, and 5:30 h, respectively after fertilization. Larvae with distinguished head, body form and tail appendage spotted between 17-22 h and the larvae started hatching at 19 h after fertilization. The average length of larvae accounted as 105.41 ± 3.73 µm. The findings of present study revealed that 0.5 mL/kg S-GnRHa could be efficient dose for successful induced breeding of A. testudineus.
... The value of fecundity is influenced by a number of issues like size, age, environmental conditions, stocking ration, and dietary constituents (Ganias, 2017;Helmizuryani et al., 2020;Tsadik & Bart, 2007). The present findings were differed from (Uddin et al., 2017) who reported that the absolute fecundity of Vietnamese koi, A. testudineus were 16,832-46,186 for 14-17 cm length and 66-89 g sized fish during his study period. ...
The present research work has been carried out to obtain evidence on breeding and embryonic growth of A. testudineus by using S-GnRHa. Fish were injected with three different doses (0.25, 0.5, and 1.0 mL/kg body weight) of synthetic hormone S-GnRHa each with three replications, where male brood fish received half of the doses of female. The fecundity of A. testudineus was ranged from 47,227 to 77,561 during the study period and except control group all the hormone received group ovulated within 12 hours of hormone injection. Among all groups, the highest fertilization rate (89.33%), highest hatching rate (79.5%) as well as highest survival rate (67.0%) was obtained at 0.5 mL/kg body weight hormone dose recipient group. The fertilized egg’s diameter was recorded as 77.59 ± 3.50 µm. The first cleavage had appeared within 18-25 min of fertilization and eventually the morula, blastula, and gastrula stages were observed at 3:10 h, 4 h, and 5:30 h, respectively after fertilization. Larvae with distinguished head, body form and tail appendage spotted between 17-22 h and the larvae started hatching at 19 h after fertilization. The average length of larvae accounted as 105.41 ± 3.73 µm. The findings of present study revealed that 0.5 mL/kg S-GnRHa could be efficient dose for successful induced breeding of A. testudineus.
... solaris (Babcock et al. 2016b). Accurate measurements of fecundity are critical for assessing population dynamics and for estimating reproductive output and how this is linked to recruitment and population irruptions (Ganias 2018). ...
Crown-of-thorns starfish (Acanthaster spp.) is reported to have exceptional reproductive capacity, but this has been largely inferred based on the overall weight of gonads (and mostly for females), and there are limited estimates of the concentration of gametes within gametogenic tissues. This study quantified gamete concentrations for both male and female Pacific crown-of-thorns starfish (Acanthaster cf. solaris), collected on Australia’s Great Barrier Reef in 2014–2019. Gamete concentrations varied greatly among female starfish (12,338–133,810 oocytes g−1), such that the estimated reproductive capacity ranged from < 1000 oocytes for the smallest (141 mm) individual up to 106 million oocytes for a 480-mm diameter female. Gamete concentrations were much more conserved for male starfish, and did not vary with size. Nonetheless, the total mass of gametogenic tissue increased with size, and fecundity of large males > 400-mm diameter approached 53 billion sperm. This study reaffirms that crown-of-thorns starfish have exceptional reproductive capacity, which is strongly size-dependent, but also varies greatly among individuals. Importantly, individual variation in reproductive output may be important in understanding for population irruptions of Acanthaster spp., and their concomitant effects on reef ecosystems.
This study explores the relationship between tolerance of corruption, in-group/out-group sensitivity to differences in random monetary distributions, and sociodemographic variables in young students in Colombia. The results offer evidence of a relationship between aversion to monetary inequity and a reduced tolerance for corrupt acts among young people. The design included two experiments: a corruption task (CT) and a sensitivity to difference in monetary rewards (MR) task. MR had two conditions, one implying social bias as a variable. Participation involved a sample of 220 students, ranging in age from fifteen to twenty-three, representing both public and private universities in Colombia. Participants with preferences for fair distributions had a lower tolerance of corruption. In this study, cognitive and sociodemographic factors influencing corruption tolerance among Colombian youth are identified. Likewise, the methodology used to investigate corruption tolerance is outlined and the mediating role of sensitivity to monetary differences in said acceptance is examined.
Subjective decisions make human cognitive processes more susceptible to bias and error. Specifically, researchers have found that additional context biases forensic anthropologists’ morphological analyses. To address whether metric analyses are also subject to bias, we conducted a pilot study in which 52 experienced osteologists measured a difficult-to-classify human femur, with or without additional contextual information. Using a metric sectioning-point sex-estimation method, participants provided a sex estimate for individual skeletal element(s) and, when given multiple elements, the combined skeletal assemblage. Control group participants (n=24) measured only the femur; and the bias participant group (n=28) were divided into female-bias (n=14) who measured the femur, a female humerus, and viewed a female-biasing photograph; and male-bias (n=14) who measured the femur, a male humerus, and viewed a male-biasing photograph. We explored whether the experts in the different groups would differ in: 1. femoral measurements; 2. femoral sex-estimation conclusions; and 3. final sex-estimation conclusions for the skeletal assemblage. Although the femoral measurements and femoral sex estimates were comparable across groups, the overall sex estimates in the female-biased group were impacted by contextual information—differing from both the control and male-biased groups (p<0.001). Our results demonstrate that cognitive bias can occur even in metric sex-estimation conclusions. Specifically, this occurred when the metric data and single-element sex estimates were synthesized into an overall estimate. Thus, our results suggest that metric methods are most vulnerable to bias when data are synthesized into an overall conclusion. These findings highlight the need for bias countermeasures and comprehensive statistical frameworks for synthesizing metric data to mitigate the effects of cognitive bias.
Due to their medicolegal repercussions, forensic anthropology conclusions must be reliable, consistent, and minimally compromised by bias. Yet, a synthetic analysis of the reliability and biasability of the discipline's methods has not yet been conducted. To do so, this study utilized Dror's (2016) hierarchy of expert performance (HEP), an eight‐level model aimed at examining intra‐ and inter‐expert reliability and biasability (the potential for cognitive bias) within the literature of forensic science disciplines. A systematic review of the forensic anthropology literature was conducted (1972‐present), including papers published in the American Journal of Physical Anthropology, Forensic Anthropology, Forensic Science International, and the Journal of Forensic Sciences and Anthropology Section abstracts published in the Proceedings of the Annual Meeting of the AAFS which matched keywords such as “forensic anthropology,” “bias,” “reliability,” “cognition,” “cognitive,” or “error.” The resulting forensic anthropology HEP showcases areas that have ample research and areas where more research can be conducted. Specifically, statistically significant increases in reliability (p < 0.001) and biasability (p < 0.001) publications were found since 2009 (publication of the NAS report). Extensive research examined the reliability of forensic anthropological observations and conclusions (n = 744 publications). However, minimal research investigated the biasability of forensic anthropological observations and conclusions (n = 20 publications). Notably, while several studies demonstrated the biasing effect of extraneous information on anthropological morphological assessments, there was no research into these effects on anthropological metric assessments. The findings revealed by the forensic anthropology HEP can help to guide future research, ultimately informing the development and refinement of best‐practice standards for the discipline.
People retrieve episodic memories about specific earlier events that happened to them. Accordingly, researchers have sought to evaluate the hypothesis that nonhumans retrieve episodic memories. The central hypothesis of an animal model of episodic memory is that, at the moment of a memory assessment, the animal retrieves a memory of the specific earlier event. Testing this hypothesis requires the elimination of nonepisodic memory hypotheses. A number of case studies focus on the development of animal models of episodic memory, including what-where-when memory, source memory, item-in-context memory, and unexpected questions. Compelling evidence for episodic memory comes from studies in which judgments of familiarity cannot produce accurate choices in memory assessments. These approaches may be used to explore the evolution of cognition.
Extensive research has documented evidence for rule learning in sequential behavior tasks in both rats and humans. We adapted the 2-choice serial multiple choice (SMC) task developed for use with rats (Fountain & Rowan, 1995a) to study sequence behavior in pigeons. Pigeons were presented with 8 disks arranged in a circular array on a touchscreen, and pecking to an illuminated disk could lead to reward. Correct responding consisted of serial patterns involving "run" chunks of 3 elements (123 234, etc.). Some pigeons experienced a violation of the chunk rule in the final chunk. Unlike rats, pigeons made fewer errors on violation chunks than run chunks, suggesting the use of low-level cues to guide choices. Removal of low-level cues and increasing the number of simultaneously illuminated disks to an 8-choice SMC task resulted in more errors on the violation chunk. Pigeons were able to use the rule when the array of disks was contracted or expanded, and when chunk length was extended to 4 and 5 elements, but not when disks were removed from or added to the array. Pigeons were also able to abstract structure from a "trill" pattern (121 232 etc.), as shown by high error rates on a violation trial. These results suggest that pigeons, like rats and humans, can abstract sequence structure, but do so primarily in the absence of specific low-level feature-based information. (PsycINFO Database Record
The long-term effects of adolescent exposure to methylphenidate (MPD) on adult cognitive capacity are largely unknown. We utilized a serial multiple choice (SMC) task, which is a sequential learning paradigm for studying complex learning, to observe the effects of methylphenidate exposure during adolescence on later serial pattern acquisition during adulthood. Following 20.0mg/kg/day MPD or saline exposure for 5days/week for 5weeks during adolescence, male rats were trained to produce a highly structured serial response pattern in an octagonal operant chamber for water reinforcement as adults. During a transfer phase, a violation to the previously-learned pattern structure was introduced as the last element of the sequential pattern. Results indicated that while rats in both groups were able to learn the training and transfer patterns, adolescent exposure to MPD impaired learning for some aspects of pattern learning in the training phase which are learned using discrimination learning or serial position learning. In contrast adolescent exposure to MPD had no effect on other aspects of pattern learning which have been shown to tap into rule learning mechanisms. Additionally, adolescent MPD exposure impaired learning for the violation element in the transfer phase. This indicates a deficit in multi-item learning previously shown to be responsible for violation element learning. Thus, these results clearly show that adolescent MPD produced multiple cognitive impairments in male rats that persisted into adulthood long after MPD exposure ended.
Copyright © 2015. Published by Elsevier Inc.
Rats were trained on an elevated maze where the rewarded alternative was defined either in terms of intra-maze cues (rubber or sandpaper flooring on rewarded and unrewarded arms, regardless of their position) or in terms of extra-maze cues (the correct arm always pointed toward a particular corner of the room, and was sometimes covered with rubber and sometimes with sandpaper), or where both sets of cues were simultaneously relevant. In Experiment 1 rats pretrained with either intra-maze or extra-maze cues alone relevant learned less about the other set of cues than non-pretrained control groups, when, in a second phase of the experiment, both sets of cues were simultaneously relevant. Experiment 2 confirmed that intra-maze cues could block extra-maze cues, and ruled out one alternative explanation of the results of Experiment 1. Experiment 3 showed that extra-maze cues overshadowed intra-maze cues, but that there was no reciprocal overshadowing of extra-maze by intra-maze cues. This was despite the fact that animals learned the intra-maze discrimination significantly faster than the extra-maze discrimination. Experiment 3 also suggested that rats did not solve the extra-maze discrimination by learning to approach or avoid specific extra-maze cues, but rather by locating the correct arm by reference to the entire set of extra-maze cues. The results suggest that locale or place learning and cue or guidance learning, in O'Keefe and Nadel's (1978) terminology, interact with one another in much the same way as does learning about any pair of stimuli in a Pavlovian conditioning experiment.
When animals code stimuli for later retrieval they can either code them in terms of the stimulus presented (as a retrospective memory) or in terms of the response or outcome anticipated (as a prospective memory). Although retrospective memory is typically assumed (as in the form of a memory trace), evidence of prospective coding has been found when response intentions and outcomes are particularly salient. At a more abstract level is the question of whether animals are able figuratively to travel back in time to recover memories of past events (episodic memory) and forward in time to predict future events (future planning). Although what would constitute adequate evidence of episodic memory and future planning is controversial, preliminary evidence suggests that animals may be capable of both forms of subjective time travel.
An African gray parrot, trained to label vocally collections of 1–6 simultaneously presented homogeneous objects, correctly identified, without further training, quantities of targeted subsets in heterogeneous collections. For each test trial the parrot was shown different collections of 4 groups of items that varied in 2 colors and 2 object categories (e.g., blue and red keys and trucks) and was asked to label the number of items uniquely defined by the conjunction of 1 color and 1 object category (e.g., "How many blue key?"). The collections were designed to provide maximal confounds (or distractions) and thus replicate the work of L. Trick and Z. Pylyshyn (1989) on humans. Humans count rather than subitize under such conditions. The parrot's results (83.3% overall accuracy) are therefore discussed in terms of their relation to human numerical competence, particularly with respect to counting. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Four major conclusions were supported in 7 runway experiments: Rats count; rats routinely and perhaps automatically count reinforcing events; counting reinforcing events is of importance for understanding instrumental learning and performance; and counting is the result of several independent coordinated cognitive processes. The results suggested counting rather than some simpler numerical ability because (a) they cannot be ascribed to other mechanisms (e.g., an identical–nonidentical discrimination or subitizing; (b) qualitatively different reinforcers were categorized as both similar and different for counting purposes; (c) the order-irrelevance principle was followed; (d) abstract tags were assigned on the basis of number of events; and (e) assignment occurred according to complex and situationally determined rules that were themselves abstract. Number cues associated with reinforcing events are often valid in learning investigations but are invariably confounded with various, equally valid number and duration cues (related to trials, responses, etc.). Reinforcers were counted when confounded with these other cues, which supported the sequential view that rats are highly disposed to using number cues associated with reinforcers and normally do so in instrumental situations. There was some evidence that one or more of the confounded events (unidentified) provided cues that were used by the rat, but this was of minor significance. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Tested 24 male albino rats on an 8-arm maze in a paradigm of sampling with replacement from a known set of items until the entire set was sampled. Exps I-III demonstrate that Ss performed efficiently, choosing an average of more than 7 different arms within the 1st 8 choices, and did not utilize intramaze cues or consistent chains of responses in solving the task. Exps IV-VI examined some characteristics of Ss' memory storage. There was a small but reliable recency effect with the likelihood of a repetition error increasing with the number of choices since the initial instance. This performance decrement was due to interference from choices rather than just to the passage of time. No evidence was found for a primary effect. The data also suggest that there was no tendency to generalize among spatially adjacent arms. Results are discussed in terms of the memory processes involved in this task and human serial learning. (27 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
A definition of counting is adopted from R. Gelman and R. M. Gallistel (1978) and Piaget (1952) that allows for a comparison between animal and human counting behavior. The evidence, which ranges from early anecdotal reports to modern experimental analyses, suggests that a variety of infrahumans ranging from birds to primates can learn to count, although successful demonstrations are most likely to occur under relatively extreme experimental conditions when alternative predictors of food or safety are unavailable. Counting behavior appears to be a relatively unnatural response in infrahumans, and its acquisition may reflect the boundaries of the animal's associative abilities. (84 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Four experiments demonstrated cross-modal transfer (CMT) of classification rules for temporal intervals. In Exp I, 20 male albino Norway rats learned a temporal discrimination between a 2- and an 8-sec signal in one modality (vision or audition). Results show positive transfer to a temporal discrimination between a 2- and an 8-sec signal in the other modality when the response rule was maintained, and negative transfer when the response rule was reversed. Exp II with 20 Ss demonstrated positive CMT in a temporal generalization procedure. Exp III demonstrated CMT of both duration and temporal location in a procedure in which 20 Ss were exposed to 3 successive signal durations. Exp IV demonstrated CMT of both duration and temporal order in a procedure in which 5 Ss were exposed to simultaneously presented signal durations, one auditory and one visual. It is concluded that rats can abstract temporal attributes from modality-specific aspects of a signal. (38 ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Three experiments examined the processes mediating rat serial pattern learning for rule-consistent versus rule-violating pattern elements ("violation elements"). In all three experiments, rats were trained to press retractable levers in a circular array in a specific sequence for brain stimulation reward (BSR). Experiment 1 examined the role of lever location (L) and element serial position (SP) cues in rats' ability to learn to anticipate a violation element positioned at the end of a 24-element serial pattern. Rats with L cues either alone or in combination with SP cues learned to anticipate the violation element, whereas those with SP cues alone did not. Rats in groups L and L+SP underwent a series of transfers designed to remove various cues that might have controlled their performance on the violation element. Results indicated that intra-chamber lever location cues mediated performance on the violation element whereas performance on rule-consistent elements within pattern chunks was mediated by an internal mnemonic representation that was insensitive to changes in lever location cues. Experiment 2 examined whether rats could learn to use SP cues alone to anticipate a violation element if it was positioned earlier in a serial pattern. Rats learned to anticipate the violation element based on SP cues alone when it was located in SP6 in a 24-element pattern, but not when it was in SP12. Experiment 3 examined whether or not rats spontaneously encode information about chunk length and the serial position of phrasing cues in serial patterns. Rats were trained to a high criterion on the serial pattern used in Experiment 1, then were challenged with three probe patterns that manipulated both chunk length and overall pattern length. Results indicated that rats spontaneously encoded information regarding the serial position of phrasing cues in relation to chunk length. Thus, rats appear to use at least three cognitive processes concurrently in serial pattern learning tasks, namely, item memory involving external discriminative cues, counting- or timing-like processes for encoding serial position, and rule abstraction for encoding an internal representation of pattern structure.
The delayed matching-to-sample (DMTS) task was used in three experiments to investigate how pigeons code information about
sample stimuli. In all experiments, each trial consisted of a signaled presentation of a sample stimulus for a fixed duration
followed, after some delay, by the presentation of three comparison stimuli. After incorrect first choices, the bird was allowed
a second choice between the remaining two stimuli. It was found, in Experiment 1, that the probability of a second choice
error declined with increasing sample duration. This result is consistent with a gradual short-term memory encoding process
but not with a simple two-state all-or-none process. In the second experiment, it was found that the distribution of first-choice
errors was affected by the particular sample occurring on a trial. This result is inconsistent with a two-stage discrete state
memory/attention model based on the assumption that encoding of the sample and attention to the comparison stimuli are both
independent all-or-none processes. The third experiment involved symbolic DMTS, in which the sample stimuli varied along a
dimension different from that along which the comparison stimuli varied. With increasing delay between sample and comparison
stimulus presentations, the pigeons were more likely to confuse test stimuli than to confuse sample stimuli. The results of
these experiments lead to the conclusion that pigeon DMTS performance depends on a gradual encoding process in which a representation
isomorphic with the test stimuli is generated and maintained.
Rats were presented with 2, 4, 6, 8, or 10 spatial locations on a 12-arm radial maze and on a subsequent test were required
to choose between a place previously visited and a novel place. The animals were reinforced for entering the novel spatial
location. During learning, animals showed an increase in errors as the number of places to be remembered increased from 2
to 8, indicating the use of a retrospective memory code. These animals also showed a decrease in errors as the number of places
to remember increased from 8 to 10, indicating the use of a prospective memory code. In an analogous mnemonic task, college
students were presented with 2, 4, 6, 8, 10, 12, or 14 Xs, shown one at a time, marked on a grid of 16 squares. On a subsequent
test, the college students were asked to choose between a novel X and one that had appeared previously. Subjects were asked
to circle the novel X. On the basis of their verbal reports, the subjects were divided into two groups reflecting different
memory coding strategies. The subjects who reported a retrospective coding strategy showed an increase in errors as the list
length increased. The subjects who reported a retrospective and prospective strategy showed an initial increase in errors
for list lengths of 2 to 8 items followed by a decrease in errors for list lengths of 8 to 14 items. The results are interpreted
to reflect a correspondence between animals and humans in the use of coding strategies aimed at facilitating memory performance
for long lists of information.
Both associative and rule-learning theories have been proposed to account for rat serial pattern learning, but individually they are unable to account for a variety of recent behavioral and psychobiological phenomena. The present study examined the role of rule learning versus discriminative learning in rat pattern learning using a classic associative phenomenon: blocking. Rats learned to press levers in an 8-lever circular array according to a rule-based serial pattern, 123-234-345-456-567-678-781-812, where digits indicate the correct lever in the array for each trial. Each pattern presentation contained a chunk with a final element violation, such as 454 instead of 456. Rats learned in a first phase that a noise signaled the violation chunk; then, a concurrent spatial cue was added in a second phase. A test with spatial cues alone showed that blocking occurred. The results suggest that associative learning mediated cuing of violation elements. Taken together with other behavioral and psychobiological evidence already reported in the literature implicating rule learning when rats learn this pattern in this paradigm, these results implicate multiple concurrent learning processes in rat serial pattern learning.
We base a theory of timing on the observation that signals of reinforcement elicit adjunctive behaviors. The transitions between these behaviors are well described as a Poisson process, with a rate constant proportional to the rate of reinforcement in the experimental context. These behaviors may come to serve as the basis for conditional discriminations of the passage of time. Varying the rate of reinforcement will generate distributions of behavior whose mean and standard deviation vary proportionately. Holding the rate of reinforcement constant while manipulating the intervals to be judged will generate different functional relations between the mean and standard deviation, and these will lead to bisection at or slightly above the geometric mean, depending on the measure of bisection employed. The correlation between the rate of the Poisson process and the rate of reinforcement implies that psychometric functions should be affected by the rate of reinforcement. This prediction is confirmed. We extend the models derived from this theory to other phenomena, such as temporal generalization and discrimination, subjective shortening, and paired comparisons of intervals. Current models of choice between delayed reinforcers are consistent with our theory of timing. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Temporal integration in duration and number discrimination by rats was investigated with the use of a psychophysical choice procedure. A response on one lever ("short" response) following a 1-s white-noise signal was followed by food reinforcement, and a response on the other lever ("long" response) following a 2-s white-noise signal was also followed by food reinforcement. Either response following a signal of one of five intermediate durations was unreinforced. This led to a psychophysical function in which the probability of a long response was related to signal duration in an ogival manner. On 2 test days, a white-noise signal with 5, 6, 7, 8, or 10 segments of either 0.5-s on and 0.5-s off or 1-s on and 1-s off was presented, and a choice response following these signals was unreinforced. The probability of a long response was the same function of a segmented signal and a continuous signal if each segment was considered equivalent to 200 ms. A quantitative fit of a scalar estimation theory suggested that the latencies to initiate temporal integration and to terminate the process are both about 200 ms, and that the same internal accumulation process can be used for counting and timing.
Five experiments determined the effects of hippocampal damage on timing and the memory for temporal events. Norway rats (N = 20) were trained to discriminate between auditory signals that differed in both duration (2 or 8 sec) and rate (2 or 16 cycles/sec). After Ss acquired the discrimination, signals with intermediate durations and rates were presented. Ss then received either fimbria-fornix lesions or control operations. Postoperatively, the accuracy of duration and rate discriminations as measured by the difference limen (DL) was unaffected by the lesion, but the point of subjective equality was shifted to a shorter duration and a slower rate by the lesion. Both Ss with lesions and Ss with control operations showed cross-modal transfer of duration and rate from the auditory signals used in training to visual signals. When a 5-sec delay was imposed between the end of a signal and the opportunity to respond, lesioned Ss were selectively impaired by the addition of the delay as measured by an increase in the DL. When a peak procedure was employed, the maximum response rate of controls was approximately at the time of scheduled reinforcement (20 sec), but the maximum response rate of lesioned Ss was earlier than the time of reinforcement. When a 5-sec gap was imposed in the signal, controls summed the signal durations before and after the gap, whereas lesioned Ss showed no retention of the signal duration prior to the gap. Lesions impaired spatial working memory in an 8-arm radial maze. (51 ref)
Electrophysiological studies have shown that single cells in the
hippocampus respond during spatial learning and
exploration1-4, some firing only when animals enter specific
and restricted areas of a familiar environment. Deficits in spatial
learning and memory are found after lesions of the hippocampus and its
extrinsic fibre connections5,6 following damage to the medial
septal nucleus which successfully disrupts the hippocampal theta
rhythm7, and in senescent rats which also show a correlated
reduction in synaptic enhancement on the perforant path input to the
hippocampus8. We now report, using a novel behavioural
procedure requiring search for a hidden goal, that, in addition to a
spatial discrimination impairment, total hippocampal lesions also cause
a profound and lasting placenavigational impairment that can be
dissociated from correlated motor, motivational and reinforcement
aspects of the procedure.
A rhesus monkey performed at high accuracy in a serial probe recognition task with color pictures as stimuli. The monkey's serial position curve was similar in form to a human's and demonstrated the theoretically important primacy and recency effects with lists containing as many as 10 or 20 items. The high accuracy of the monkey was shown to be largely due to the minimization of proactive interference through the use of more than 200 distinct items. These results encourage the view of similar mechanisms of memory in monkey and humans.
In 3 experiments, rats and humans learned serial patterns composed of 24, 30, or 36 items. Patterns had a 2-, 3-, or 4-level hierarchical rule structure. In Experiments 1 and 2, patterns had either perfect hierarchical structure or 2 modified chunks that violated hierarchical structure, thus producing linear structure (i.e., nonhierarchical structure). For both rats and humans, pattern structure predicted pattern learning difficulty and also the nature and relative frequency of errors. Both treated chunks that were inconsistent with hierarchical structure as violation chunks, that is, they made errors that reflected their "tendency to regularize the perception of an irregular pattern" (F. Restle & B. L. Burnside, 1972). The results support the view that rats can abstract and encode a representation of multilevel hierarchical structure in serial patterns in much the same way as humans do in analogous tasks.
Rats learned serial patterns composed of either "run" chunks (e.g., 123 234 ...) or "trill" chunks (e.g., 121 232 ...). For each type of pattern, 1 group of rats encountered an element at the end of the pattern that violated the run or trill structure. In both run and trill patterns, violations were unusually difficult for rats to learn, whereas corresponding elements in "perfect" patterns that did not violate pattern structure were easy. Additionally, rats' errors on violation elements conformed to the structure of the patterns in which they were embedded. Thus, rats were sensitive to the run or trill organization of their patterns and mastered the rules governing the pattern before learning "exceptions to the rule."
This paper describes circumstances around the discovery of long-term potentiation (LTP). In 1966, I had just begun independent work for the degree of Dr medicinae (PhD) in Per Andersen's laboratory in Oslo after an eighteen-month apprenticeship with him. Studying the effects of activating the perforant path to dentate granule cells in the hippocampus of anaesthetized rabbits, I observed that brief trains of stimuli resulted in increased efficiency of transmission at the perforant path-granule cell synapses that could last for hours. In 1968, Tim Bliss came to Per Andersen's laboratory to learn about the hippocampus and field potential recording for studies of possible memory mechanisms. The two of us then followed up my preliminary results from 1966 and did the experiments that resulted in a paper that is now properly considered to be the basic reference for the discovery of LTP.
Two experiments investigated how brief pauses introduced into serial patterns as phrasing cues would affect pattern learning in rats. In Experiment 1, a 24-element pattern consisted of eight 3-element chunks, whereas a 20-element pattern consisted of four 5-element chunks. In both patterns, 3.0-s temporal pauses placed at chunk boundaries (synchronous phrasing cues) facilitated learning compared to no phrasing. Cues "out of sync" with pattern structure (asynchronous phrasing cues) facilitated learning for the 24-element pattern and retarded learning for the 20-element pattern. Evidence suggested that in the latter case, 3.0-s pauses served as "blank" trials that induced rats to "skip" to the next serial position in sequence. In Experiment 2, shorter 0.5-s pauses served as phrasing cues in the 20-element pattern of Experiment 1. Synchronous short cues facilitated learning, whereas asynchronous phrasing cues had no effect. Furthermore, removal of synchronous cues produced deficits in performance on formerly cued trials, whereas removal of asynchronous cues had no effect. The results of Experiment 2 support the notion that in both experiments phrasing cues served as discriminative cues and indirectly suggest that rats are concurrently sensitive to pattern element cues, extra-sequence cues (such as phrasing cues), and to the relative timing of sequential events.
Recursive, hierarchically organized serial patterns provide the underlying structure in many cognitive and motor domains including speech, language, music, social interaction, and motor action. We investigated whether learning of hierarchical patterns emerges in infancy by habituating 204 infants to different hierarchical serial patterns and then testing for discrimination and generalization of such patterns. Results indicated that 8- to 10-month-old and 12- to 14-month-old infants exhibited sensitivity to the difference between hierarchical and non-hierarchical structure but that 4- to 6-month-old infants did not. These findings demonstrate that the ability to perceive, learn, and generalize recursive, hierarchical, pattern rules emerges in infancy and add to growing evidence that general-purpose pattern learning mechanisms emerge during the first year of life.
The present study examined the effects of systemically administered atropine sulfate, a muscarinic cholinergic antagonist, on a series of probe tests in the retention of a highly-structured serial pattern in a serial multiple choice (SMC) task. Rats were trained on a 24-element pattern composed of eight 3-element chunks ending with a violation element: 123-234-345-456-567-678-781-818 where the digits represent the clockwise position of levers in an octagonal chamber, dashes indicate 3-s pauses termed “phrasing cues,” and other intertrial intervals were 1 s. In daily acquisition trials rats were given either 50 mg/kg of atropine sulfate or an equivalent amount of saline (Chenoweth & Fountain, 2015). Following acquisition, rats were given a series of drug challenges, and the present study reports a series of Phrasing Cue Removal Probes that tested rats’ abilities to make correct responses in the absence of phrasing cues. Rats tested under atropine demonstrated more difficulty in recalling encoded responses in these probe trials than did rats tested under saline. The results indicate that intact central muscarinic cholinergic systems were needed for rats to display efficient adaptive response strategies under conditions where some features of the previously-learned pattern change.
The current experiment examined the factors that determine acquisition for elements of highly structured serial patterns. Three groups of rats were trained on three patterns with parallel rule-based hierarchical structure, but with 3-, 4-, or 5-element chunks, each with a final violation element. Once rats mastered their patterns, probe patterns were introduced to answer several questions. To assess the extent to which the learned response pattern depended on intrachamber location cues for anticipating different element types, Spatial Shift Probes shifted the starting lever of patterns to locations that positioned chunk boundaries where they had never been experienced during training. To assess the extent to which a phrasing cue is necessary for rats to perform a chunk-boundary response, a Cue Removal Probe tested whether rats would produce a chunk-boundary response in the correct serial position if the phrasing cue was omitted. To assess the extent to which cues from multiple trials leading up to the violation element are required to anticipate the violation element, Multiple-Item Memory Probes required rats to make an unexpected response on one of the elements in the last two chunks of the pattern prior to the violation element. The results indicated that rats used multiple concurrent learning and memory processes to master serial patterns, including discrimination learning, rule learning, encoding of chunk length, and multiple-item memories.
For decades, beginning with Lashley’s (1951) celebrated paper or even earlier with the work of Ebbinghaus and others (Hunter, 1920; Skinner, 1934), sequential learning has repeatedly aroused debate over the fundamental nature of learning, memory, and representation in humans and animals. In recent years, debate has centered on whether nonhuman animals can use nonassociative symbolic processes such as rule-induction to learn about the structure of patterned sequences (“serial patterns”) of events. The work by Hulse and colleagues on rats’ serial-pattern learning (SPL) of food reward magnitude in runways, in particular, supported a Rule-Learning (RL) theory (e.g., Hulse & Campbell, 1975; Hulse & Dorsky, 1977; Hulse, 1978; Hulse & Dorsky, 1979; Fountain & Hulse, 1981; Fountain, Evensen, & Hulse, 1983). The RL theory proposed that rats learned some representation of the abstract rules that described organized sequences (Fountain, 1986; Roitblat, Pologe, & Scopatz, 1983; Wathen & Roberts, 1994). The implication was that rats did not have to rely on chaining or remote associations alone to master sequences. Later work in our laboratory involved a somewhat different SPL paradigm employing patterns of stimuli drawn from another stimulus dimension (viz., a spatial dimension rather than food reward magnitude). This work also supported the RL view of serial-pattern learning in both rats and mice (e.g., Fountain, 1990; Fountain & Rowan, 1995b; Fountain & Rowan, 1995a).
Three experiments investigated the role of NMDA receptor dependent systems in sequential learning and memory. Rats tracked serial patterns after systemic administration of MK-801, an NMDA receptor antagonist that blocks plasticity in the hippocampus and other structures. Experiments 1 and 2 sought to describe the effects of MK-801 on acquisition and retention of serial patterns. Patterns were 24 elements long and highly organized, with some groups receiving a 'violation' element that did not fit the organization of the rest of the pattern. Experiment 3 evaluated MK-801's effects on the integration of new information that was either consistent or inconsistent with a previously learned pattern structure. The results of these experiments indicated that MK-801 interfered with serial pattern learning and, to a lesser degree, retention. Learning about structure was relatively spared, whereas learning about interruptions or violations of pattern structure was impaired. The latter differential effects are consistent with the contention in earlier literature that serial pattern learning is subserved by at least two learning/memory systems.
Atropine sulfate is a muscarinic cholinergic antagonist which impairs acquisition and retention performance on a variety of cognitive tasks. The present study examined the effects of atropine on acquisition and retention of a highly-structured serial pattern in a serial multiple choice (SMC) task. Rats were given daily intraperitoneal injections of either saline or atropine sulfate (50 mg/kg) and trained in an octagonal operant chamber equipped with a lever on each wall. They learned to press the levers in a particular order (the serial pattern) for brain-stimulation reward in a discrete-trial procedure with correction. The two groups learned a pattern composed of eight 3-element chunks ending with a violation element: 123-234-345-456-567-678-781-818 where the digits represent the clock-wise positions of levers in the chamber, dashes indicate 3-s pauses, and other intertrial intervals were 1 s. Central muscarinic cholinergic blockade by atropine caused profound impairments during acquisition, specifically in the encoding of chunk-boundary elements (the first element of chunks) and the violation element of the pattern, but had a significant but negligible effect on the encoding of within-chunk elements relative to saline-injected rats. These effects persisted when atropine was removed, and similar impairments were also observed in retention performance. The results indicate that intact central muscarinic cholinergic systems are necessary for learning and producing appropriate responses at places in sequences where pattern structure changes. The results also provide further evidence that multiple cognitive systems are recruited to learn and perform within-chunk, chunk-boundary, and violation elements of a serial pattern.
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Two experiments examined whether rats could learn a rule-based response sequence when prevented from performing a consistent motor pattern. In a serial multiple-choice procedure, rats chose from an 8-lever array mounted on the walls of an octagonal operant chamber. In Experiment 1, rats learned to choose levers in proper order according to one of two patterns, a structured pattern, 1-2-3-4-5-6-7-8, or an unstructured pattern, 1-7-3-5-6-4-2-8, where digits indicate the clockwise position of correct levers in the circular array. These patterns were interleaved with random elements consisting of levers drawn from the set of all 8 possible positions in the array. Rats in the structured group learned their pattern, indicating that they were not limited to learning response sequences based on a consistent motor pattern. Furthermore, rats learned the structured pattern much faster than the unstructured pattern, indicating that pattern structure facilitated learning. To test the notion that the random elements of Experiment 1 may have slowed learning by creating structural ambiguity caused by irrelevant structural relations, in Experiment 2 irrelevant relations were minimized by ensuring that the correct pattern- and random-element responses were spatially distant from one another. Rats again learned the structured pattern faster than the unstructured pattern and, additionally, faster than the structured pattern in Experiment 1. The results of both experiments indicate that even when prevented from performing a consistent motor pattern and irrelevant relationships are present between pattern elements, rats abstract and encode rules describing structured sequential patterns.
Two experiments examined whether muscarinic cholinergic systems play a role in rats' ability to perform well-learned highly-structured serial response patterns, particularly focusing on rats' performance on pattern elements learned by encoding rules versus by acquisition of stimulus-response (S-R) associations. Rats performed serial patterns of responses in a serial multiple choice task in an 8-lever circular array for hypothalamic brain-stimulation reward. Two experiments examined the effects of atropine, a centrally-acting muscarinic cholinergic receptor antagonist, on rats' ability to perform pattern elements where responses were controlled by rules versus elements, such as rule-inconsistent "violation elements" and elements following "phrasing cues," where responses were controlled by associative cues. In Experiment 1, 3-element chunks of both patterns were signaled by pauses that served as phrasing cues before chunk-boundary elements, but one pattern also included a violation element that was inconsistent with pattern structure. Once rats reached a high criterion of performance, the drug challenge was intraperitoneal injection of a single dose of 50 mg/kg atropine sulfate. Atropine impaired performance on elements learned by S-R learning, namely, chunk-boundary elements and the violation element, but had no effect on performance of rule-based within-chunk elements. In Experiment 2, patterns were phrased and unphrased perfect patterns (i.e., without violation elements). To control for peripheral effects of atropine, rats were treated with a series of doses of either centrally-acting atropine or peripherally-acting atropine methyl nitrate (AMN), which does not cross the blood-brain barrier. Once rats reached a high criterion, the drug challenges were on alternate days in the order 50, 25, and 100 mg/kg of either atropine sulfate or AMN. Atropine, but not AMN, impaired performance in the phrased perfect pattern for pattern elements where S-R associations were important for performance, namely, chunk-boundary elements. However, in the structurally more ambiguous unphrased perfect pattern where rats had fewer cues and presumably relied more on S-R associations throughout, atropine impaired performance on all pattern elements. Thus, intact muscarinic cholinergic systems were shown to be necessary for discriminative control previously established by S-R learning, but were not necessary for rule-based serial pattern performance.
This study was designed to determine whether deficits in adult serial pattern learning caused by adolescent nicotine exposure persist as impairments in asymptotic performance, whether adolescent nicotine exposure differentially retards learning about pattern elements that are inconsistent with "perfect" pattern structure, and whether there are sex differences in rats' response to adolescent nicotine exposure as assessed by a serial multiple choice task. The current study replicated the results of our initial report (Fountain, Rowan, Kelley, Willey, & Nolley, 2008) using this task by showing that adolescent nicotine exposure (1.0mg/kg/day nicotine for 35days) produced a specific cognitive impairment in male rats that persisted into adulthood at least a month after adolescent nicotine exposure ended. In addition, sex differences were observed even in controls, with additional evidence that adolescent nicotine exposure significantly impaired learning relative to same-sex controls for chunk boundary elements in males and for violation elements in females. All nicotine-induced impairments were overcome by additional training so that groups did not differ at asymptote. An examination of the types of errors rats made indicated that adolescent nicotine exposure slowed learning without affecting rats' cognitive strategy in the task. This data pattern suggests that exposure to nicotine in adolescence may have impaired different aspects of adult stimulus-response discrimination learning processes in males and females, but left abstract rule learning processes relatively spared in both sexes. These effects converge with other findings in the field and reinforce the concern that adolescent nicotine exposure poses an important threat to cognitive capacity in adulthood.
Work on experimental manipulations that affect chunking in sequential learning has shown that cues inserted into a sequence, termed “phrasing cues,” can facilitate learning. Two experiments examined how temporal intervals positioned at chunk boundaries facilitate serial-pattern learning. Experiment 1 showed that rat serial-pattern learning can be facilitated when distinct temporal intervals precede chunk boundaries regardless of whether the intervals are longer or shorter than intervals within chunks. Experiment 2 replicated the acquisition results of Experiment 1 with a different serial pattern. In addition, after both 14 and 35 days of acquisition with phrasing cues, cue removal produced severe deficits in tracking Element 1 of chunks, the element directly after the phrasing cues during acquisition. All in all, the results indicate that rats used both short and long temporal phrasing intervals as discriminative cues and that facilitated learning due to phrasing is not the result of additional processing time provided by longer intertrial intervals at chunk boundaries. Furthermore, many of the finer details of the results could be accounted for by the additional assumption that phrasing cues overshadow interitem associations.
In each of two investigations, rats ran in a runway to obtain varying quantities of food pellets presented in a fixed order,
such as 20-0-20. The major finding was that rats ran faster on a 0-pellet trial if that trial was followed shortly by a 20-pellet
trial (e.g., 20-0-20 series) than if it was not (e.g., 20-0 series). This finding was obtained both within groups (Experiment
1) and between groups (Experiment 2), and suggested that the memory of 20 pellets arising from the first trial of the 20-0-20
series was retrieved not only on the second trial of the series, thereby signaling 0 pellets, but on the third trial as well,
thereby also signaling 20 pellets. Retrieving the memory of 20 pellets on Trial 3 of the 20-0-20 series apparently resulted
in that memory’s elevating speed on Trial 2 of that series.
The effect of intertrial interval, preset interval, and retention interval on the performance of rats in a time estimation task was described. On each trial a signal was presented for a duration of 2 to 8 sec. Eighteen rats were trained to press one lever (the short response) if the signal was shorter than 4 sec, and another lever (the long response) if the signal was longer than 4 sec. When trials were massed (Experiment 1), the percentage long response was affected by the classification of the previous signal, but not by its actual duration. This suggests that the animals remembered the response made on the previous trial, but not the signal duration. If a response was not permitted on the previous trial (Experiment 2), the duration or classification of the previous signal had no effect on performance. This supports the conclusion from the first experiment and suggests that an animal can reset its internal clock in less than 2 sec. In Experiment 3, the difference limen of the psychophysical function increased with the duration of the retention interval, but the point of subjective equality did not change. This suggests that resetting of the internal clock occurs on a non-time dimension.
Hersh (Mem Cogn 2:771-774, 1974) investigated the role of irrelevant relations in college students' pattern learning and performance for letter series completion problems. He created irrelevant relations in sequences by inserting items to make pattern structure ambiguous such that it was open to multiple interpretations during initial pattern processing. He reported irrelevant relations impaired humans' performance more when placed at the beginning of patterns than at the end. However, once pattern structure was induced, irrelevant relations were not impairing. Here, we examined the impact on rat serial pattern learning of irrelevant relations positioned at the beginning or end of a serial pattern. Rats pressed levers in a circular array according to the same structured serial pattern, 123 234 345 456 567, where digits indicated the clockwise position of the correct lever. This structured serial pattern was interleaved with repeating responses on lever 2 to produce irrelevant relations at the beginning of the pattern (Beginning: 122232 223242 324252 425262 526272), on lever 6 to produce irrelevant relations at the end of the pattern (End: 162636 263646 364656 465666 566676), or on lever 8 to produce no irrelevant relations (No Irrelevant Relations: 182838 283848 384858 485868 586878. Irrelevant relations significantly retarded learning regardless of their placement within the pattern. However, irrelevant relations retarded learning significantly more when placed at the pattern beginning versus end. The results indicate that rats, like humans, process patterns from beginning to end.
Episodic memory consists of representations of specific episodes that happened in the past. Modeling episodic memory in animals requires careful examination of alternative explanations of performance. Putative evidence of episodic-like memory may be based on encoding failure or expectations derived from well-learned semantic rules. In Experiment 1, rats were tested in a radial maze with study and test phases separated by a retention interval. The replenishment of chocolate (at its study-phase location) depended on two factors: time of day (morning vs. afternoon) and the presence or absence of chocolate pellets at the start of the test phase. Because replenishment could not be decoded until the test phase, rats were required to encode the study episode. Success in this task rules out encoding failure. In Experiment 2, two identical mazes in different rooms were used. Chocolate replenishment was trained in one room, and then they were asked to report about a recent event in a different room, where they had no expectation that the memory assessment would occur. Rats successfully answered the unexpected question, ruling out use of expectations derived from well-learned semantic rules. Our behavioral methods for modeling episodic memory may have broad application for assessments of genetic, neuroanatomical, neurochemical, and neurophysiological bases of both episodic memory and memory disorders such as those that occur in Alzheimer's disease.
A rhesus monkey correctly recognized 86 and 81 percent of 10- and 20-item lists, respectively. It serial position curve was similar in form to a human's curve, revealing prominent primacy and recency effects. The key to these findings was in minimizing proactive interference through the use of a large pool of 211 color photographs.
The authors evaluated the ontogenetic performance of a grey parrot (Psittacus erithacus) on object permanence tasks designed for human infants. Testing began when the bird was 8 weeks old, prior to fledging and weaning. Because adult grey parrots understand complex invisible displacements (I. M. Pepperberg & F. A. Kozak, 1986), the authors continued weekly testing until the current subject completed all of I. C. Uzgiris and J. Hunt's (1975) Scale 1 tasks. Stage 6 object permanence with respect to these tasks emerged at 22 weeks, after the bird had fledged but before it was completely weaned. Although the parrot progressed more rapidly overall than other species that have been tested ontogenetically, the subject similarly exhibited a behavioral plateau part way through the study. Additional tests, administered at 8 and 12 months as well as to an adult grey parrot, demonstrated, respectively, that these birds have some representation of a hidden object and understand advanced invisible displacements.
Ordinal, interval, and circadian mechanisms of solving a time-place task were tested. Rats searched for food twice in the morning and once in the afternoon (Group AB-C, n = 5) or once in the morning and twice in the afternoon (Group A-BC, n = 5) in a box with four food troughs. The location of the food depended on the time of day in a 12:12-h light:dark cycle. Acquisition was documented by food-site inspections at the correct locations prior to food availability. On nonrewarded probes, the time of the middle search (B) was shifted late (for Group AB-C) or early (for Group A-BC). The rats visited Location B at chance, contrary to an ordinal mechanism. When the posttesting meal and light-dark transitions were omitted, the rats visited correct locations with impaired performance but at above-chance levels on nonrewarded probes. The results are consistent with interval and circadian representations of time.
The term "theory" is taken to refer "to any explanation of an observed fact which appeals to events taking place somewhere else, at some other level of observation, described in different terms, and measured, if at all, in different dimensions." Learning theory to date has tended to create a false sense of security, and research designed with respect to it is likely to be wasteful. Extensive examples are given to show that productive research can proceed from the study of a datum which varies in a significant fashion. At present, little effective use is made of empirical or rational equations. There seems to be no a priori reason why a complete account of the higher mental processes is not possible without appeal to theoretical processes in other dimensional systems.
A fundamental question in comparative cognition is whether animals remember unique, personal past experiences. It has long been argued that memories for specific events (referred to as episodic memory) are unique to humans. Recently, considerable evidence has accumulated to show that food-storing birds possess critical behavioral elements of episodic memory, referred to as episodic-like memory in acknowledgment of the fact that behavioral criteria do not assess subjective experiences. Here we show that rats have a detailed representation of remembered events and meet behavioral criteria for episodic-like memory. We provided rats with access to locations baited with distinctive (e.g., grape and raspberry) or nondistinctive (regular chow) flavors. Locations with a distinctive flavor replenished after a long but not a short delay, and locations with the nondistinctive flavor never replenished. One distinctive flavor was devalued after encoding its location by prefeeding that flavor (satiation) or by pairing it with lithium chloride (acquired taste aversion), while the other distinctive flavor was not devalued. The rats selectively decreased revisits to the devalued distinctive flavor but not to the nondevalued distinctive flavor. The present studies demonstrate that rats selectively encode the content of episodic-like memories.
1. Three mutations which eliminate specific types of photoreceptors in Drosophila were characterized.
2. Of the eight photoreceptors in each facet, two mutations delete the outer six (R 1‐6). The third eliminates R 7, one of the two central photoreceptors. Double mutants can be constructed in which only photoreceptor R 8 is present.
3. The spectral sensitivities, photopigments, and behavioural properties of these mutants were investigated.
4. R 1‐6 have two sensitivity peaks, near 350 and 470 nm. These receptors contain a rhodopsin with these absorption peaks. It interconverts with a metarhodopsin that absorbs around 570 nm.
5. R 7 is a U.V.‐receptor, containing rhodopsin that absorbs around 370 nm and interconverts with a metarhodopsin which absorbs around 470 nm.
6. R 8 is a non‐adapting blue‐receptor with a third type of rhodopsin.
7. The properties of these photopigments explain the different sensitivities and spectral adaptation phenomena of the various photoreceptors.
8. All the photoreceptors have input into phototaxis. Spectral analysis of this behaviour provides evidence for integration of the input from the different photoreceptors.