Robert D. Nebes’s research while affiliated with Duke University Medical Center and other places

On psychometric tests, spatial scores typically decline more with age than do verbal scores. Since in humans, visuo-spatial information is more efficiently processed by the right hemisphere (RH) and verbal information by the left (LH), this behavioral pattern could reflect a greater age decline in RH than in LH abilities. To test this possibility, the speed with which young and old subjects identified stimuli in their right and left visual fields was measured. Since each half field, projects to the opposite hemisphere, by presenting stimuli in one half field, RH and LH abilities can be measured relatively independently. Words were identified faster in the right field (i.e., LH), pictorial stimuli in the left (RH). This was equally true for both young and old. Similarly, a right ear advantage in the identification of dichotically presented syllables was of equal magnitude in both age groups. Thus, there was no evidence on these tasks for a selective decline with age in RH processing efficiency.

A deficit in focused attention has recently been suggested to underlie some of the cognitive decrements seen in the elderly. This hypothesis was tested in two visual search studies. Subjects had to decide whether or not a given target was present among an array of six digits, three of which were red, the rest black. For the "yes" trials, prior information regarding target color substantially reduced search time in comparison to warning signal that did not provide color information. This reduction in search time was equivalent in the young and the old, both at long (ad lib) and shorter (250-1000 msec) array durations. This result suggests that both age groups are equally proficient in focusing their attention on the digits of the relevant color. On the "no" trials, prior color-information was not effective in reducing search time. There was some evidence in experiment two that the older subjects were using a different search strategy on these trials.

In the present experiment, subjects decided on each trial whether or not a unilaterally presented probe digit was a member of a previously memorized set of two, three, or four digits. The probe was presented at a near-threshold duration and followed by a visual pattern mask. Signal-detection estimates of detectability and response bias were obtained from subjects' confidence ratings regarding their decisions. The detectability of the probe in memory was significantly better when the probe was presented to the right visual field-left hemisphere than when presented to the left visual field-right hemisphere. The response criterion became significantly more lax as memory-set size increased, but only for probes presented to the left visual field-right hemisphere. The present results are consistent with reaction-time studies using verbal stimuli that indicate a left hemisphere advantage in the efficiency of memory comparison.

The present study investigated whether there is a differential decline with age in verbal and spatial memory, by measuring the ability of 24 young (mean age = 18.8) and 24 elderly (mean age = 69.5) subjects to remember verbal and spatial information under identical task conditions. Subjects recalled either the identities or spatial locations of seven letters arranged randomly within a 5 x 5 grid. To determine whether subjects actually encoded the verbal and spatial characteristics of the array differently, verbal and spatial interference tasks were administered during the retention interval. Results showed that the memory decrement in the elderly was not greater for the spatial aspects of the stimulus array than for its verbal aspects. Thus, there was no evidence for a greater decline with age in spatial memory than in verbal memory. Limited support was found for the utility of the selective interference paradigm to demonstrate separate and independent verbal and spatial memory codes.

The decrease in response speed usually found to occur with advancing age is felt by many investigators to be a phenomenon common to all speeded tasks, regardless of the exact nature of the sensory stimulus or motor response involved. In the present experiment, however, the type of response the subject made determined whether or not an age difference existed in simple reaction time to a visual stimulus. When subjects responded manually, by releasing a key, the usual age decrement in response latency was found. When the same subjects responded vocally, by saying a word, there was no significant age difference in reaction time. This result suggests that slowing of psychomotor latency with age is not a general phenomenon, but may be limited to certain neural systems.

Right, mixed and left-handed college students were given the complete WAIS, and a series of cognitive factor tests. Results showed left- and mixed-handed individuals to have a significantly lower full scale I.Q. than right-handers. There was no difference between the mixed and left-handers. In all three handedness groups, subjects with a positive family history of sinistrality had a lower full scale I.Q. than did subjects without left-handed relatives. Neither handedness nor family history differentially affected the Verbal or Performance subscales, nor did they have a significant effect on scores in the other cognitive tests. These results are discussed with respect to Levy's theory of hemispheric specialization, and to the role of inheritance and brain damage in the causation of left- and mixed-handedness.Presently at the Department of Psychiatry, University of Pittsburgh School of MedicinePresently at the Hospital for Sick Children, Toronto, Ontario, Canada.

Older individuals have been reported to use imagery mediation less often than the young in remembering verbal material. To determine whether this is due to a decrease with age in the speed with which verbal stimuli are recoded into pictorial representations, the reaction time of 12 old (63-78) and 12 young (17-25) subjects for matching verbal descriptions to geometric shapes was measured. While the elderly were generally slower, they were identical to the young in being faster at determining whether or not two simultaneously presented shapes were the same than they were a printed description of a shape and a shape. Also, in both age groups, when 1 or more sec elapsed between the presentation of the description and that of the shape, matching times were as quick as when both stimuli were shapes, suggesting that, for the old as well as the young, 1 sec was sufficient time to recode the description into a pictorial form.

To test the hypothesis that older persons tend not to use verbal mediators in paired-associate learning because it takes them too long to form an appropriate mediator, the time needed by young and old subjects to generate sentences incorporating given pairs of nouns was measured. Older subjects formed sentences just as rapidly as did the young. Despite their equivalent speed in creating these verbal associations when tested later for the occurrence of incidental learning of the noun pairs, the older subjects showed much poorer recall than did the younger subjects. This age difference in learning did not appear to be a function of any major dissimilarities in the generated sentences themselves, i.e., in the grammatical constructions used, or in the imageability of the relationships expressed by the sentences. The rated imagery value of the stimulus nouns was found to affect both the speed of sentence formation and the accuracy of incidental learning; in both younger and older subjects, formation time was less, and recall was better for the high imagery noun pairs.

Right and left handers were given a variety of memory tasks for which imagery ability has been demonstrated to be an important determinant of performance. Results showed no significant relationship between subjects' handedness and the efficiency with which they used imagery in memory.

The effects of handedness, family history of handedness, sex, and ear differences on the performance of a dichotic listening task by 120 college students were studied. The sample, as a whole, showed a significant right ear superiority. Females made fewer errors than males. There were no significant main effects of family history or handedness nor were any of the interactions significant. It was suggested that right ear dominance is more prevalent than is generally supposed. A possible relationship between ear asymmetries and intellectual level was discussed.