Selective attention affects implicit and explicit memory for familiar pictures at different delay conditions.
ABSTRACT Three experiments investigated the effects of two variables -selective attention during encoding and delay between study and test- on implicit (picture fragment completion and object naming) and explicit (free recall and recognition) memory tests. Experiments 1 and 2 consistently indicated that (a) at all delays (immediate to 1 month), picture-fragment identification threshold was lower for the attended than the unattended pictures; (b) the attended pictures were recalled and recognized better than the unattended; and (c) attention and delay interacted in both memory tests. For implicit memory, performance decreased as delay increased for both attended and unattended pictures, but priming was more pronounced and lasted longer for the attended pictures; it was still present after a 1-month delay. For explicit memory, performance decreased as delay increased for attended pictures, but for unattended pictures performance was consistent throughout delay. By using a perceptual object naming task, Experiment 3 showed reliable implicit and explicit memory for attended but not for unattended pictures. This study indicates that picture repetition priming requires attention at the time of study and that neither delay nor attention dissociate performance in explicit and implicit memory tests; both types of memory require attention, but explicit memory does so to a larger degree.
- SourceAvailable from: link.springer.com[show abstract] [hide abstract]
ABSTRACT: The effects of memory for unattended events—for example, events that occur while a person is asleep, anesthetized, or selectively attending to other ongoing events, as in a speech-shadowing task—are rarely revealed in tests of retention that require remembering to be deliberate or intentional. Might such effects become evident in tests that do not demand awareness of remembering? Results of the present shadowing study, involving the recognition and spelling of previously unattended homophones, suggest an affirmative answer to this question.Memory & Cognition 04/1984; 12(2):105-11. · 1.92 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Two experiments investigated the possibility that perceptual memory for words is dependent on level of awareness of those words. In Experiment 1, subjects attempted to report briefly exposed words in a study phase and then identify words that faded into view in a test phase. Old words appeared in both the study and test phases, whereas new words appeared only in the test phase. Perceptual memory, indexed as the faster identification of old vs. new words, was observed only for words correctly reported in the study phase. In the study phase of Experiment 2, words were flanked by digits, and the distribution of attention between words and digits was varied. Perceptual memory increased from nil to high levels as more attention was allocated to the words. These findings suggest that long-term perceptual memory is dependent on level of awareness of words in the study phase.Journal of Experimental Psychology Human Perception & Performance 09/1991; 17(3):807-15. · 2.40 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: This study is the first to report complete priming in Alzheimer's disease (AD) patients and older control subjects for objects presented haptically. To investigate possible dissociations between implicit and explicit objects representations, young adults, Alzheimer's patients, and older controls performed a speeded object naming task followed by a recognition task. Similar haptic priming was exhibited by the three groups, although young adults responded faster than the two older groups. Furthermore, there was no difference in performance between the two healthy groups. On the other hand, younger and older healthy adults did not differ on explicit recognition while, as expected, AD patients were highly impaired. The double dissociation suggests that different memory systems mediate both types of memory tasks. The preservation of intact haptic priming in AD provides strong support to the idea that object implicit memory is mediated by a memory system that is different from the medial-temporal diencephalic system underlying explicit memory, which is impaired early in AD. Recent imaging and behavioral studies suggest that the implicit memory system may depend on extrastriate areas of the occipital cortex although somatosensory cortical mechanisms may also be involved.Neuropsychologia 02/2004; 42(8):1063-70. · 3.48 Impact Factor
Soledad Ballesteros Selective attention and implicit memory - 1
Selective attention affects implicit and explicit memory for
familiar pictures at different delay conditions
José M. Reales
Dpto. de Psychología, Universidad Nacional de Educación a Distancia, Spain
Dept. of Psychology, New York University
Running title: Selective attention and implicit memory
Key words: selective attention, delay, implicit memory, explicit memory, picture-
fragment-completion, recognition, free-recall.
This study was supported by the Dirección General de Investigación Científica y
Técnica (DGICYT Grant PB94-0393) to SB and the National Science Foundation
(NYI Grant SBR-9528197) to MC. Experiments1 and 2 were presented at the
38th (1997) and 40th (1999) Annual Meetings of the Psychonomic Society.
Correspondence: Marisa Carrasco, Dept. of Psychology, New York University, 6
Washington Pl., NY NY 10003; email@example.com
Soledad Ballesteros Selective attention and implicit memory - 2
Three experiments investigated the effects of two variables –selective attention
during encoding and delay between study and test– on implicit (picture fragment
completion and object naming) and explicit (free recall and recognition) memory
tests. Experiments 1 and 2 consistently indicate that: a) at all delays (immediate to
1 month), picture-fragment identification threshold was lower for the attended than
the unattended pictures; b) the attended pictures were recalled and recognized
better than the unattended; c) attention and delay interacted in both memory tests:
For implicit memory, performance decreased as delay increased for both attended
and unattended pictures, but priming was more pronounced and lasted longer for
the attended pictures; it was still present at 1-month delay. For explicit memory,
performance decreased as delay increased for attended pictures, but for unattended
pictures performance was consistently throughout delay. By using a perceptual
object naming task, Experiment 3 showed reliable implicit and explicit memory for
attended but not for unattended pictures. This study indicates that picture
repetition priming requires attention at the time of study and that neither delay nor
attention dissociate performance in explicit and implicit memory tests; both types
of memory require attention, but explicit memory does so to a larger degree.
Soledad Ballesteros Selective attention and implicit memory - 3
Selective attention affects implicit and explicit memory for familiar
pictures at different delays
It is widely accepted that there are two manifestations of memory, explicit and
implicit. However, the role of some variables considered to dissociate these two
types of memory has been questioned. In particular, the role of attention and of delay
between study and test in implicit memory remain controversial. Attention is required
for the formation of enduring memory traces in explicit memory (e.g., Baddeley et al.
1984; Broadbent, 1958; Craik et al. 1996; Fisk & Schneider, 1984; Mulligan, 1998;
Rock & Gutman, 1981; Shiffrin & Schneider, 1977). However, the role that attention
plays in implicit memory is not well understood. Its effects may depend on stimulus
duration at study (e.g., Ganor-Stern, Seamon & Carrasco, 1998; Weldon & Jackson-
Barrett, 1993), type of stimuli (Smith & Oscar-Berman, 1990; Wolters & Prinsen,
1997), type of test employed (Mulligan & Hartman, 1996), attentional load
(Mulligan, 1997), and the way attention is manipulated (Crabb & Dark, 1999;
MacDonald & MacLeod, 1998; Wood, Stadler, & Cowan, 1997).
A number of studies using the divided attention paradigm at encoding have
shown that whereas attention impairs performance on explicit and conceptual implicit
memory tests (e.g., Jacoby, Lindsey, & Toth, 1992; Jacoby, Toth, & Yonelinas, 1993;
Mulligan 1997, 1998, Mulligan & Harman, 1996; but see Isingrini, Leroy & Vazou,
1995), it has little or no effect on perceptual implicit memory tests (e.g., Parkin &
Russo, 1990; Parkin, Reid, & Russo, 1990; Russo & Parkin, 1993). On the other
hand, recent selective attention studies in the verbal domain have found attentional
effects in both explicit and implicit memory (e.g. Clarys, Isingrini & Haerty, 2000;
Crabb & Dark, 1999; MacDonald & MacLeod, 1998; Stone et al., 1998). However,
the role of selective attention in implicit memory for visual pictures has not been
Soledad Ballesteros Selective attention and implicit memory - 4
The goal of this study was to investigate the role of selective attention at
encoding on implicit and explicit memory tests for visual objects using a novel
overlapping-picture task. To our knowledge, this is the first study to evaluate the
effects of selective attention at encoding on implicit tests –picture fragment
completion and speeded object naming– and explicit memory –free recall and
recognition– for pictures. Furthermore, to examine whether attention and delay
interact both implicit and explicit memory were assessed at several delays between
study and test – from immediate to a month. Because attention at encoding
strengthens stimulus representation (e.g. Carrasco, Penpeci-Talgar & Eckstein,
2000; Ganor-Stern et al., 1998; Kinchla, 1992; Posner, 1980; Rock & Gutman,
1981), we hypothesized that attended material may be more resilient to the passage
of time so that performance in both implicit and explicit memory tasks would be
superior and last longer for attended than unattended pictures.
Explicit versus implicit memory
Explicit memory is typically assessed by direct tests of memory such as free
recall, cued recall, and recognition, whereas implicit memory is measured by
indirect memory tests that do not ask subjects to recollect specific prior
experiences. Implicit memory is inferred when subjects show facilitation in
performance that is attributable to information acquired during the study phase.
This facilitation, often referred to as repetition priming, has been found in several
tests using verbal materials; e.g., word identification (e.g., Graf & Schachter,
1985; Graf & Ryan, 1990; Jacoby & Dallas, 1981), word-stem completion (e.g.,
Roediger & Blaxton, 1987; Schacter & Graf, 1989), word-fragment completion
Soledad Ballesteros Selective attention and implicit memory - 5
(e.g., Tulving, Schacter & Stark, 1982), and word/nonword decision (e.g.,
Kirsner, Milech & Standen, 1983). More recently, a number of visual studies have
focused on nonverbal materials, such as possible/impossible judgments of 3-D
novel visual patterns (e.g., Carrasco & Seamon, 1996; Schacter, Cooper &
Delaney, 1990), object naming (e.g., Biederman & Cooper, 1991; Reales &
Ballesteros, 1999; Srinivas, 1993), drawing of 2-D novel visual patterns (Musen &
Treisman, 1990), symmetrical/asymmetrical judgments of visual patterns (e.g.,
Ballesteros & Cooper, 1992), or judgments of affective preference (e.g., Seamon
et al., 1995). Implicit memory is also manifested in audition (Schacter & Church,
1992), touch (Ballesteros, 1994; Ballesteros, Reales, & Manga, 1999) and cross-
modally (Easton, Srinivas & Greene, 1997; Reales & Ballesteros, 1999).
A number of experimental variables dissociates explicit and implicit memory;
e.g., stimulus encoding instructions (e.g., Schacter, Cooper, & Delaney, 1990),
study-test changes in the stimuli (e.g., size, orientation, mode of exploration;
Cooper, Schacter, Ballesteros, & Moore, 1992; Seamon et al., 1995), length of
retention interval (e.g., Musen & Treisman, 1990; Snodgrass & Surprenant, 1989;
Tulving, Schacter, & Stark, 1982), and degree of attention during study (e.g.,
Parkin & Russo, 1990). Research on functional memory dissociations has been
comprehensively reviewed (e.g., Graf, 1994; Moscovitch, Goshen-Gottstein &
Vriezen, 1994; Richardson-Klavehn & Bjork , 1988; Roediger & McDermott,
1993; Schacter, 1987, 1994; Schacter, Chiu, & Ochsner, 1993). However, a series
of studies has questioned the generalizability of these dissociations (e.g., Bentin et
al., 1998; Carrasco & Seamon, 1996; Ganor-Stern et al., 1998; MacDonald &
MacLeod, 1998; Reales & Ballesteros, 1999; Roediger, 1990; Snodgrass &
Soledad Ballesteros Selective attention and implicit memory - 6
Supranant, 1989; Wood et al., 1997). In this study, we assessed whether attention,
delay, and/or their interaction dissociate implicit and explicit memory performance.
The role of attention in perceptual implicit memory for verbal materials.
Verbal studies disagree as to whether perceptual implicit memory requires
the participation of attention. Some authors have asserted that attention is not
necessary for implicit memory. They base their conclusion on studies using
selective attention and shadowing prose (Eich, 1984) and lexical decision
(Szymanski & MacLeod, 1996) tasks, or divided attention and word-fragment
completion (Parkin et al., 1990). In contrast, others have concluded that attention
is necessary for the emergence of implicit memory. This conclusion has been
reached by using a selective attention paradigm and tasks such as lexical decision
(Bentin, Moscovitch, & Nirhod, 1998), word-identification priming (Stone et al.,
1998), word-stem completion and perceptual fluency (Crabb & Dark, 1999), rapid
reading (MacDonald & MacLeod, 1998), and words-digits flanking (Hawley &
Johnston, 1991), as well as a divided attention paradigm and a shadowing task
with a rapid presentation rate (Wood et al., 1997). These studies on verbal implicit
memory tests indicated that attention is necessary at encoding to establish a lasting
representation that can support repetition priming. These verbal perceptual priming
studies indicate that implicit and explicit memory for words cannot longer be
distinguished on the grounds that attentional manipulations affect performance on
explicit but not on implicit tests.
The role of attention in perceptual implicit memory for object pictures.
Soledad Ballesteros Selective attention and implicit memory - 7
Most studies of attention and memory have used words as stimuli; only few
studies have used pictures. As is the case with verbal studies, object pictures
studies are inconsistent with regard to the role of attention in implicit memory.
Whereas some authors have reported that attention dissociates explicit and implicit
memory (e.g., Parkin & Russo,1990; Russo & Parkin, 1993), some have reached
the opposite conclusion (Ganor-Stern et al., 1998).
Parkin and Russo (1990) and Russo and Parkin (1993) found that divided
attention significantly impaired explicit memory (recall) but not implicit memory
(picture-fragment completion). The authors concluded that this implicit memory
test reflects the influence of automatic processes, which are considered to take
place without attentional participation.
It has been suggested that attention can have qualitatively similar but
quantitatively different effects on explicit and implicit memory; implicit memory is
less sensitive to attentional manipulations than explicit memory, but that does not
imply that implicit memory is attention free (Ganor-Stern et al., 1998). By studying
the effects of limited attentional resources at study time on explicit and implicit
memory, these authors found that when attention at study was limited by a
flanking-digits procedure, object recognition was diminished but object decision
priming for possible pictures was unaffected. However, when study time was
Soledad Ballesteros Selective attention and implicit memory - 8
reduced from 5 to 3 sec, object recognition was still diminished and object priming
was eliminated. Hence, the degree to which priming is affected by attentional
resources was determined by the intervening variable of study time; implicit
memory was more sensitive to an attentional manipulation when study time was
The effect of delay in implicit and explicit memory
Delay between study and test has often been used to explore the functional
dissociation between implicit and explicit memory tests (Roediger & McDermott,
1993). Although a number of studies have reported that such a dissociation has
emerged as a function of delay (e.g., McAndrews, Glisky, & Schacter, 1987;
Reales & Ballesteros, 1999; Sloman et al. 1988), there is no consensus on this
topic (e.g., Snodgrass & Surprenant, 1989).
According to Jacoby and Dallas (1981) retention interval dissociates explicit
and implicit memory. Whereas the former decreased in a 24-hr delay; the latter was
still present at such delay. Tulving and colleagues (Tulving et al., 1982) showed
that while recognition memory declined sharply over a week, priming assessed by
the word fragment completion decreased only by 3 %. Following those two
seminal studies, others have explored the effect of delay. There is a stable
repetition priming but a diminished recognition for familiar pictures between 1 and
6 weeks (Mitchell & Brown, 1988). Similarly, even for nonsense patterns
perceptual priming remains approximately constant from a few hours to a week
delay. The recognition results, on the other hand, indicated that explicit memory
decreased significantly with time (Musen & Treisman, 1990).. Likewise, both
Soledad Ballesteros Selective attention and implicit memory - 9
within-modal (vision/vision) and cross-modal (touch/vision) priming are both
unaffected at a 30 min delay, whereas explicit recall decreases significantly at such
a delay (Reales & Ballesteros, 1999).
Other studies, however, showed significant losses of priming over a week
delay. For instance, priming drops about 25% (Sloman, et al., 1988) to about 50%
(Light, Singh & Capps, 1986; Roediger & Blaxton, 1987). It is noteworthy that
using word fragment completion there was an initial 5-min period of rapid
forgetting, and then a very slow decay rate, to the point that priming was still
present after 16 months of study (Sloman et al., 1988).
Snodgrass and Supranant's study (1989), however, did not provide evidence
for the dissociation of implicit and explicit memory as a function of delay.
Performance for a picture-fragment completion implicit memory task and for a
yes/no recognition explicit task showed approximately equal rates of forgetting up
to a delay of 14 days (for similar results see Lachman & Lachman, 1980).
In short, the functional dissociation between implicit and explicit memory as
a function of retention interval is not unequivocal. To further evaluate this
dissociation, in this study we explored whether selective attention at encoding
affects similarly explicit and implicit memories at different delays.
The present study
We investigated whether the effects of selective attention and study-test
delay interact on explicit and implicit memory. We hypothesized that if attended
information attains a stronger representation than unattended information (e.g.,
Desimone & Duncan, 1995; Ganor-Stern et al., 1998; Posner, 1980; Rock &
Gutman, 1981; Yeshurun & Carrasco, 1998, 1999), the former should be more
Soledad Ballesteros Selective attention and implicit memory - 10
resilient to time passage and consequently delay should affect it less. Furthermore,
if priming for unattended pictures occurs it should diminish or disappear earlier
than for attended pictures. Note that even if the representation of both attended
and unattended pictures decays at a similar rate, the representation would fall
below identification threshold earlier for the unattended than attended pictures
because the initial representation for the attended pictures is stronger.
Divided attention studies have some methodological limitations. A slow rate
of presentation could allow subjects to switch attention between attended and
unattended information thus enabling performance in implicit but not in explicit
memory tests (Bentin et al., 1998; Cowan, 1995; Crabb & Dark, 1999; MacDonald
& MacLeod, 1998). In addition, most of the studies reporting no effect of
attention in implicit memory have used tasks in which target and distracting stimuli
were presented in different sensory modalities –audition and vision, and it is likely
that attention may tax resources more within than between modalities.
To evaluate the implicit/explicit dissociation while circumventing these
methodological problems, Experiments 1 and 2 explored the effects of selective
attention at encoding on implicit and explicit memory at several delay conditions
(immediate, 5 min, 1 day, 1 week, and 1 month). In this selective attention
paradigm with overlapping figures, participants are directed to attend to the figure
of a given color; no information is provided regarding the figure of the other color.
Using this paradigm it has been found that attended pictures are highly recognized
but unattended ones are not (Goldstein & Finke, 1981; Rock & Gutman, 1981).
In the first two experiments we manipulated selective attention at encoding
Soledad Ballesteros Selective attention and implicit memory - 11
by using superimposed outlines of pictures (Rock & Gutman, 1981) and we tested
implicit memory by using fragmented pictures of the same objects (Snodgrass et
al., 1987; Snodgrass & Supranat, 1989). In Experiment 3 we manipulated selective
attention at encoding in the same way but implicit memory was assessed by using a
speeded object naming task. Explicit memory was assessed either by a recall
(Experiment 1) or recognition (Experiment 2 and 3) tests.
Like Rock and Gutman (1981) we used overlapped pictures, but unlike them
we used pictures of familiar pictures. Research using overlapped figures has
shown that the representations activated by the attended stimuli are stronger than
those activated by the unattended pictures.i Observers were presented with two
overlapping pictures of two different colors and were required to name the object
of one specific color. Observers were asked to maintain fixation in the center of
the two figures. Even if eye movements were to occur the pictures overlapped so
that the attended one would not have an advantage in terms of retinal location
(Rock & Gutman, 1981). Furthermore, the two overlapping pictures had different
colors so that the outlines could be easily discriminated as belonging to different
pictures. Color is known to facilitate the organization of items; groups of items
resulting from color similarity are often treated as units (e.g., Bundesen &
Pedersen, 1983; Carrasco & Chang, 1995; Kahneman & Henik, 1981).
This experiment assessed the role of selective attention in both implicit and
explicit memory tasks at several delays ranging from 0-min to 1-month. The
i Note that, even though we used overlapped figures, our procedure is not related to that of Tipper (1985).
We used no probes, and for the same observer a figure could only be attended, unattended or nonstudied;
i.e. an attended figure could have not been unattended in the previous trial. Consequently, no negative
priming could be expected (see Procedures).
Soledad Ballesteros Selective attention and implicit memory - 12
implicit test of speeded-picture fragment completion was administered before the
explicit test of free recall at all delays.
Participants. Sixty males, 18 to 21 ys. old, voluntarily participated in one or
two 45-min experimental sessions, depending on the delay condition they were
assigned to. Because they were fulfilling the Spanish Obligatory Military Service
and they lived in an assigned barrack the experimenter could recruit them as
experimental conditions required, without previous notice. All had normal or
corrected to normal vision and were naive as to the purposes of the study. They
had never participated in any other perception or cognition experiment.
Apparatus. The stimuli were presented on a 14" color monitor of a
Compatible PC 486 computer, whose resolution was 640 x 480 pixels. The
system was interfaced with a voice-key (Lafayette 63040) to record at what level
of completion the picture was named.
Stimuli. Ninety stimuli selected from Snodgrass and Vanderwart (1980)
picture set. The pictures were approximately 10 x 10 cm subtending a visual angle
of approximately 4 x 4°. During the study phase the pictures were depicted with a
continuous green or blue outline (Figure 1); during the test phase the stimuli were
fragmented black outlines of the stimuli (Snodgrass et al. 1987) presented on white
Insert Figures 1 & 2
The pictures were digitized, saved on graphic BMP format and presented on
the computer monitor. A 16 x 16 grid was simulated and it was superimposed to
the projected image. All the 16 x 16 pixel blocks that contained some black pixels
Soledad Ballesteros Selective attention and implicit memory - 13
were identified. This information was stored in an array and was randomly
permuted. The deleted block rate of the image followed from the exponent
function: P = 0.7 x e 8.0
Each picture was stored as fragmented images at eight different levels of
completion (Figure 2). Level 1 corresponded to the most fragmented image
whereas level 8 was the complete picture. The proportion of deleted pixel blocks
was 0.91, 0.88, 0.83, 0.76, 0.65, 0.51, 0.30, and 0 from levels 1 to 8, respectively.
Design. A mixed-factorial design was used: 2 within-subject factors –3
study conditions (attended, unattended and non-studied pictures) x 2 types of test
(implicit vs. explicit)– and 1 between-subject factor: 5 delay conditions (non-
delayed, 5 min, 1 day, 1 week and 1 month).
Procedure. The 90 stimuli were randomly divided in three groups of 30
pictures. For counterbalancing purposes, each of these groups appeared as the
attended (green), unattended (blue), or non-studied (black) pictures for 4
observers in each delay condition.ii During the study phase participants performed
a speeded-naming task –they were asked to name as soon as possible the identity
of the green picture. The participant pressed the mouse button when he was ready.
After 1500 ms, two overlapped pictures appeared at the center of the screen, one
in blue and the other in green. Then, the participant named the green pictures as
ii Previous research has shown that the particular color of the attended or unattended object is not a critical
variable (Rock & Gutman, 1981).
Soledad Ballesteros Selective attention and implicit memory - 14
quickly as possible. Both pictures disappeared from the screen as soon as the
response was made. Finally, the experimenter typed the object’s name. There
were 30 experimental trials. In addition, to avoid primacy and recency effects,
observers performed 5 extra trials at the beginning and 5 at the end from the same
set of pictures. Participants identified correctly all the pictures. This study phase
lasted approximately between 5 and 6 min.
After completing the study phase, according to the delay condition they were
assigned to, all observers participated in the test phase, in which they performed a
speeded fragment completion task (Snodgrass et al., 1987). Observers were
presented with progressively less fragmented pictures. Once each fragmented
picture appeared on the screen, if participants did not respond for 1.5 sec the next
more completed level was shown. They were asked to identify each object as soon
as possible, by pressing the space key of the keyboard as soon as they identified
the object. A prompt on the screen indicated that they should type the object's
name. There were 90 trials in which the pictures were sequentially presented for
1.5 sec at each of the eight-fragmented levels. The sequence stopped when the
observers started to type the name of the object. The order of presentation of the
90 pictures –30 attended, 30 unattended and 30 non-studied– was randomized for
each participant. Performance was assessed by the fragmentation level at which
Soledad Ballesteros Selective attention and implicit memory - 15
the pictures were correctly identified, which the computer recorded. If the name
was incorrect, the computer beeped and the next more completed level
automatically appeared. After a 2 sec interval, another picture was randomly
selected. There were 5 practice trials at the beginning. Even though participants
did not know that a second phase would follow, to prevent rehearsal, participants
assigned to the 5-min condition were asked to write down as many names of
Spanish soccer players as possible. This test phase lasted approximately 40 min.
Lastly, explicit memory was evaluated by asking participants to type on the
keyboard the name of as many pictures as possible that they had seen during the
study phase. Participants were required to complete this free-recall task in 5-min.
Performance was assessed by the total number of correct attended pictures, correct
unattended pictures and intrusions (non-studied pictures).
RESULTS and DISCUSSION
1) Picture fragment completion test
1.1) Absolute identification thresholds. The superior performance for the
attended pictures is evident by the lower threshold for picture identification (Figure
3). The pictures were identified under more degraded conditions when observers
had named the pictures during the study phase, than when they had either not
named them (unattended) or not seen them (non-studied). This result was