Aspects of Code-Specific Memory Development

We investigated the development of code specific representations of different kinds of information in long term memory. Forty second graders, 40 sixth graders and 40 adults learned the associations between 12 pictures and one position each in a 4 × 3 grid of squares, 12 pictures and 1 of 12 monosyllabic words each or 12 pictures and 1 of 12 faces. After a 3 min distractor task, a picture was presented in the retrieval phase, and the associated position, word or face had to be selected. Performance in the verbal condition improved as a function of age, while performance in the spatial condition turned out to be independent of age, and the performance in the facial condition showed a difference between both child groups and the adults. The results revealed a developmental difference of code specific representation of different kinds of information.     

Is there evidence for automatic processing of spatial and color attributes present in pictures and words?

The current experiment studies evidence for automatic processing of color and spatial dimensions present in matched pictures and words. Subjects studied four lists of either line drawings or matched words that varied in color (red or green) and position (left or right side), under one of four encoding conditions. Subjects were instructed to encode (1) only the item, (2) the item and its color, 13) the item and its position, or (4) the item and both color and position. All subjects participated in an unexpected final recognition task in which item recognition and recall for both attributes, regardless of original encoding instructions, we:re examined. Color memory appeared to be effortful for both pictures and words, as it was at chance level unless subjects were specifically instructed to encode the information. Position was most poorly recalled when subjects attended only to item information, but memory for this dimension was well above chance in all encoding conditions. The position of the line drawings was better recalled than the position of the words. The implications of these results for Hasher and Zacks’ (1979) model of automatic processes is discussed.     

Predictive inferences take time to develop

In order to determine the time course of inferences about predictable events, predicting or control contexts were presented, followed by a target word (Exps. 1A, B, and C) or a continuation sentence (Exp. 2) that confirmed or disconfirmed the predicted event. Relative to the control condition, under the predicting condition there was facilitation in naming the confirming target words 1500 ms after the onset of the last word in the context (Exp. 1C), but not after 500 ms (Exp. 1A), and only a tendency after 1000 ms (Exp. 1B). In addition, there was facilitation in reading the post-target and final regions of the continuation sentence that confirmed the predicted event, as well as inhibition when the predicted event was disconfirmed, but no effect was observed on the target word itself (Exp. 2). It is concluded that, when the predicted event is highly constrained by the context, predictive inferences are likely to be drawn on-line, but they take time to construct. Received: 14 January 1998 / Accepted: 21 April 1998     

Implicit memory for new associations: The pictorial influence

A series of experiments was conducted in order to show that implicit memory for new associations is not always dependent on semantic integrative processing during study. The material used in these experiments differed from traditional studies that employed pairs of unrelated words. Instead, targets (words in Exps. 1 and 2 and pictures in Exps. 3 and 4) were encoded in the context of an unrelated picture. The implicit tests used were word-stem completion (Exps. 1, 2, and 3) and picture-fragment identification (Exp. 4). The explicit test was word-stem cued recall (Exps. 1, 2, and 3) and picture-fragment cued recall (Exp 4). For implicit tests, context effects were not obtained using words as targets with a non-integrative semantic-elaboration encoding task (Exp. 1). When an integrative semantic-elaboration encoding task was used, a standard context effect emerged (Exp. 2) for implicit memory. Importantly, with pictures as targets, context effects appeared without integrative semantic encoding (Exps. 3 and 4). However, context effects were obtained for all conditions of cued recall. Results are discussed with regard to the concept of unitization.     

Source attributions and false memories: a test of the demand characteristics account

When lists of related words are presented to subjects, they sometimes recall or recognize nonpresented words related to those lists (critical lures). In fact, subjects sometimes claim to remember which of two speakers said the critical lures. We examined whether this finding could be accounted for by demand characteristics. If subjects’ willingness to make source attributions to critical lures reflects experimental demand, one would predict that subjects should be willing to change and should have little confidence in these attributions. Subjects made more attributions, were less likely to change their attributions, and were more confident in their attributions for critical lures than for unrelated distractors. Subjects had even more confidence in the attributions that they made for words that had actually been presented, and they were even less likely to change these attributions. These findings suggest that false memories are quite compelling but that they are also subtly different from true memories.     

Is judgment of random time intervals biased and capacity-limited?

 Recently, random generation of time intervals has been proposed as a procedure to impair executive processing in a dual-task paradigm without substantial interference with phonological and visuo-spatial working memory resources. A fundamental assumption of this procedure is that humans are able to distinguish time sequences on their degree of randomness. The present study tests this assumption. To this end, non-biased, repetition-biased, alternation-biased sequences and repetitive rhythms were judged under conditions of higher or lower executive load. In Exp. 1, load depended on the presentation speed, while in Exp. 2, a dual-task condition was used with either a concurrent number-copying task or an arithmetic task. It was found that the participants could distinguish repetitive rhythms from more or less random sequences, and that both accuracy of this judgment and latency were affected by the concurrent load. The findings are taken as a first indication that random time judgment is capacity-limited. Received: 9 September 1999 / Accepted: 1 October 1999     

Semantic priming occurs for word but not location pronunciation in the postcue task

Semantic priming refers to the finding that a word response is facilitated if it is preceded by a related word compared to when it is preceded by an unrelated word. Dallas and Merikle (Can J Psychol 30: 15–21 1976a; Bull Psychon Soc 8: 441–444 1976b) demonstrated that semantic priming occurred under conditions in which a pair of simultaneously displayed words was previewed for over a second prior to the onset of a cue indicating which of the words should be pronounced aloud (postcue task). In contrast, semantic interference effects have been reported for postcue picture-naming tasks (Dean et al. in J Exp Psychol Learn Mem Cogn 27: 733–743, 2001; Humphreys et al. in J Exp Psychol Learn Mem Cogn 21: 961–980, 1995). According to Dean et al., the semantic interference effects in postcue picture naming occur because the integration of the object and the cued attribute in memory is more difficult for categorically related pictures than for unrelated pictures. The aim of this experiment was to determine whether this idea was true for postcue word pronunciation tasks. Participants completed two postcue tasks, one requiring pronunciation of the target word indicated by a locational cue and another requiring pronunciation of the location of a centrally presented word. Results indicated a semantic priming effect only for the locational cue condition suggesting that the integration of the cue and identity information was unaffected by word context. These data suggest that priming in a postcue word pronunciation task may be due to feedback from residual activation within the semantic system facilitating access to the target word’s phonology.     

Effects of contextual and local factors on Ponzo illusion magnitude

Ponzo illusion has been explained by considering either just the inducing elements present in a restricted area of the visual field, the same area in which the test elements are located, or the stimulus configuration as a whole in which even the most distal figural elements – i.e., the external converging lines, here called “Ponzo wedge”– play a crucial role. The two studies reported here aimed at showing that both global configurational characteristics and inducing elements locally interacting with the test stimuli can independently affect the illusory effect. This hypothesis was tested using stimuli in which graphic-inducing elements giving rise to a herringbone pattern (Coren & Girgus, 1978) were drawn in the same area of the test segments. Results of Exp. 1 confirmed the effect of the two factors. In particular, both factors proved to determine the illusion, since they induced illusory effects either in isolation or in the same/opposite direction. In Exp. 2 the relative weight of these two factors was evaluated in relation to the width of the angle of the inducing elements and to the distance of the test segments from the vertex. Results showed no linear relationships between the distance of the test segments from the external inducing elements and the weight of the Ponzo wedge factor. Received: 25 June 1996 / Accepted: 1 October 1997     

Comparing black-capped (Poecile atricapillus) and mountain chickadees (Poecile gambeli): use of geometric and featural information in a spatial orientation task

Since Cheng (Cognition 23:149–178, 1986) first proposed the “geometric module” in rats, a great deal of research has focused on how other species use geometric information and how geometric encoding may differ across species. Here, hand-reared and wild-caught black-capped chickadees and wild-caught mountain chickadees searched for food hidden in one corner in a rectangular environment. Previous research has shown that mountain chickadees do not spontaneously encode geometric information when a salient feature is present near the goal location. Using a slightly different training and testing procedure, we found that both hand-reared and wild-caught black-capped chickadees encoded geometric information, even in the presence of a salient landmark. Some, but not all, mountain chickadees also encoded geometric information. Overall, our results suggest that use of geometric information may be a less preferred strategy for mountain chickadees than for either wild-caught or hand-reared black-capped chickadees. To our knowledge, this is the first direct interspecies comparison of use of geometric information in a spatial orientation task.     

Interference from short-term memory processing on encoding and reproducing brief durations

A temporal reproduction task is composed of two temporal estimation phases: encoding of the interval to be reproduced, followed by its reproduction. The effect of short-term memory processing on each of these phases was tested in two experiments. In Exp. 1, a memory set was presented, followed by two successive tones bounding the target interval to be reproduced. During the reproduction of the target interval, a probe was presented, and the subject ended the reproduction by pressing one of two keys, depending on the presence or absence of the probe in the memory set. In Exp. 2, probe recognition was required during the encoding of the interval to be reproduced. Whereas in Exp. 1 reproductions lengthened as a function of memory-set size, in Exp. 2 temporal reproductions decreased with set size. These results support attentional models of time estimation and suggest that short-term memory processing interrupts concurrent accumulation of temporal information. Received: 11 September 1997 / Accepted: 2 March 1998     

Reversing presentation order of semantically related words reverses memory

In the Deese-Roediger-McDermott paradigm, words (e.g., sour, candy, sugar,…) related to one critical word (e.g., sweet) typically are encoded in descending order of their association with the critical word. When recognition is tested, memory is greater for related words than for critical words, as predicted by extant memory models. Surprisingly, however, memory is not greater for unrelated words (presented in other encoding lists) than for related words, in contrast with predictions from these same models. In two experiments, we tested whether intralist presentation order is responsible for the unexplained results. Word lists were studied in standard or reversed order (ascending order of association to critical words). Subsequent recognition for related words was high when lists were presented in the standard order but very low when lists were presented in reverse. Results indicate that presentation order affects related-word false alarms, providing important new constraints for memory models.     

The cumulative semantic cost does not reflect lexical selection by competition

The cumulative semantic cost describes a phenomenon in which picture naming latencies increase monotonically with each additional within-category item that is named in a sequence of pictures. Here we test whether the cumulative semantic cost requires the assumption of lexical selection by competition. In Experiment 1 participants named a sequence of pictures, while in Experiment 2 participants named words instead of pictures, preceded by a gender marked determiner. We replicate the basic cumulative semantic cost with pictures (Exp. 1) and show that there is no cumulative semantic cost for word targets (Exp. 2). This pattern was replicated in Experiment 3 in which pictures and words were named along with their gender marked definite determiner, and were intermingled within the same experimental design. In addition, Experiment 3 showed that while picture naming induces a cumulative semantic cost for subsequently named words, word naming does not induce a cumulative semantic cost for subsequently named pictures. These findings suggest that the cumulative semantic cost arises prior to lexical selection and that the effect arises due to incremental changes to the connection weights between semantic and lexical representations.     

The modulation of lexical competition by segment duration

In an eye-tracking study, we examined how fine-grained phonetic detail, such as segment duration, influences the lexical competition process during spoken word recognition. Dutch listeners’ eye movements to pictures of four objects were monitored as they heard sentences in which a stop-initial target word (e.g.,pijp “pipe”) was preceded by an [s]. The participants made more fixations to pictures of cluster-initial words (e.g.,spijker “nail”) when they heard a long [s] (mean duration, 103 msec) than when they heard a short [s] (mean duration, 73 msec). Conversely, the participants made more fixations to pictures of the stop-initial words when they heard a short [s] than when they heard a long [s]. Lexical competition between stop- and cluster-initial words, therefore, is modulated by segment duration differences of only 30 msec.     

Scanning two memorized lists

Subjects were timed as they decided whether singly presented probe words belonged to one or the other of two memorized lists, or to neither list. Each list varied in length from one to four words. Reaction times increased linearly with the combined number of words in the two lists. When there was no a priori basis for distinguishing the lists, the slope of the function for positive test probes was 33–35 msec per word higher than that for negative probes. The slope for negative probes was 58 msec per word in one experiment and 46 msec per word in another. This suggests that subjects first scanned the combined lists exhaustively to determine whether the probe was present; if it was not, they made a negative response, and if it was, they scanned again to determine which list it was in. When the words in the two lists were conceptually distinct (one list representing animate and the other inanimate objects), the difference in slope was reduced to only 6 msec per word, suggesting that the second scan was all but eliminated.     

Spatial range of illusory effects in Müller-Lyer figures

The spatial range of the illusory effects in Müller-Lyer (M-L) figures was examined in three experiments. Experiments 1 and 2 assessed the pattern of bisection errors along the shaft of the standard or double-angle (experiment 1) and the single-angle (experiment 2) M-L figures: Subjects bisected the shaft and the resulting two half-segments of the shaft to produce apparently equal quarters, and then each of the quarters to produce eight equal-appearing segments. The bisection judgments of each segment were referenced to the segment's physical midpoints. The expansion or wings-out and the contraction or wings-in figures yielded similar patterns of bisection errors. For the standard M-L figures, there were significant errors in bisecting each half, and each end-quarter, but not the two central quarters of the shaft. For the single-angle M-L figures, there were significant errors in bisecting the length of the shaft, the half-segment, and the quarter, of the shaft adjacent to the vertex but not the second quarter from the vertex nor in dividing the half of the shaft at the open end of the figure into four equal intervals. Experiment 3 assessed the apparent length of the half-segment of the shaft at the open end of the single-angle figures. Length judgments were unaffected by the vertex at the opposite end of the shaft. Taken together, the results indicate that the length distortions in both the standard and single-angle M-L figures are not uniformly distributed along the shaft but rather are confined mainly to the quarters adjacent to the vertices. The present findings imply that theories of the M-L illusion which assume uniform expansion or contraction of the shafts are incomplete. Received: 15 December 2000 / Accepted: 5 June 2001     

Episodic encoding and recognition of pictures and words: role of the human medial temporal lobes

In the present PET study, we examined brain activity related to processing of pictures and printed words in episodic memory. Our goal was to determine how the perceptual format of objects (verbal versus pictorial) is reflected in the neural organization of episodic memory for common objects. We investigated this issue in relation to encoding and recognition with a particular focus on medial temporal-lobe (MTL) structures. At encoding, participants saw pictures of objects or their written names and were asked to make semantic judgments. At recognition, participants made yes-no recognition judgments in four different conditions. In two conditions, target items were pictures of objects; these objects had originally been encoded either in picture or in word format. In two other conditions, target items were words; they also denoted objects originally encoded either as pictures or as words. Our data show that right MTL structures are differentially involved in picture processing during encoding and recognition. A posterior MTL region showed higher activation in response to the presentation of pictures than of words across all conditions. During encoding, this region may be involved in setting up a representation of the perceptual information that comprises the picture. At recognition, it may play a role in guiding retrieval processes based on the perceptual input, i.e. the retrieval cue. Another more anterior right MTL region was found to be differentially involved in recognition of objects that had been encoded as pictures, irrespective of whether the retrieval cue provided was pictorial or verbal in nature; this region may be involved in accessing stored pictorial representations. Our results suggest that left MTL structures contribute to picture processing only during encoding. Some regions in the left MTL showed an involvement in semantic encoding that was picture specific; others showed a task-specific involvement across pictures and words. Together, our results provide evidence that the involvement of some but not all MTL regions in episodic encoding and recognition is format specific.     

Concept formation and categorization of complex,asymmetric, and impossible figures

Impossible figures are striking examples of inconsistencies between global and local perceptual structures, in which the overall spatial configuration of the depicted image does not yield a coherent three-dimensional object. In order to investigate whether structural “impossibility” is an important perceptual property of depicted objects, we used a category formation task in which subjects were asked to divide pictures of shapes into groups that seemed most natural to them. Category formation is usually unidimensional, such that sorting is dominated by a single perceptual property, so this task can serve as a measure of which dimensions are most salient. In Experiment 1, subjects received sets of 12 line drawings consisting of six possible and six impossible objects. Very few subjects grouped the figures by impossibility on the first try, and only half did so after multiple attempts at sorting. In Experiment 2, we investigated other global properties of figures: symmetry and complexity. Subjects readily sorted objects by complexity, but seldom by symmetry. In Experiment 3, subjects were asked to draw each of the figures before sorting them, which had only a minimal effect on categorization. Finally, in Experiment 4, subjects were explicitly instructed to divide the shapes by symmetry or impossibility. Performance on this task was perfect for symmetry, but not for impossibility. Although global properties of figures seem extremely important to our perception, the results suggest that some of these cues are not immediately obvious or salient for most observers.     

The influence of theme identifiability

In the present study, we used the Deese/Roediger-McDermott paradigm to analyze the relationship between theme identifiability of word lists and false memories in adults and children. We conducted two normative studies to determine the identifiability levels for critical unpresented words in 40 associative lists in adults and in 16 associative lists in children. Then, in three experiments, false memories for critical words that were either easy or hard to identify were analyzed in adults and in children 4–5 years old and 11–12 years old. Opposite results were found for adults and children. Lists with highly identifiable critical words produced fewer false memories for adults but more false memories for children. These results suggest that, if they can identify critical words, adults use an identify-to-reject strategy to edit out false memories, whereas, in children, theme identification does not lead to the use of such a monitoring strategy.     

Physical and conceptual priming effects on picture and word identification

In the study phase of these experiments, subjects were asked to think of an item suggested by the omission in an incomplete sentence, and then look at a picture or word describing an item and say whether it was the same as theirs. In the test phase, they were asked to identify studied and nonstudied items presented briefly in either picture or word form. Subjects were then required to recall the words or pictures shown in the study phase. Experiment 1, with a within-subjects design, revealed that the studied pictures were identified more readily than studied words and nonstudied pictures. This indicates a physical priming effect. In word identification, studied words were identified more readily than nonstudied words; however, there was no difference between studied words and studied pictures, and the performance for studied pictures and nonstudied items were largely the same. The physical priming effect on picture identification was also shown in Experiment 2, with a between-subjects design. Different processing mechanisms in picture and word identification are discussed.