The CA3 network as a memory store for spatial representations

Comparative neuroanatomy suggests that the CA3 region of the mammalian hippocampus is directly homologous with the medio-dorsal pallium in birds and reptiles, with which it largely shares the basic organization of primitive cortex. Autoassociative memory models, which are generically applicable to cortical networks, then help assess how well CA3 may process information and what the crucial hurdles are that it may face. The analysis of such models points at spatial memories as posing a special challenge, both in terms of the attractor dynamics they can induce and how they may be established. Addressing such a challenge may have favored the evolution of elements of hippocampal organization observed only in mammals.     

Semantic memory and verbal working memory correlates of N400 to subordinate homographs

N400 is an event-related brain potential that indexes operations in semantic memory conceptual space, whether elicited by language or some other representation (e.g., drawings). Language models typically propose three stages: lexical access or orthographic- and phonological-level analysis; lexical selection or word-level meaning and associate activation; and lexical integration, sentence- and discourse-level operations. The exact stage that N400 reflects is unknown, although opinion favors lexical integration over lexical selection. Surprisingly, little research has assessed relationships between neuropsychological measures of semantic memory fund of information or verbal working memory capacity and N400. Subjects performed a homograph disambiguation comprehension task with minimal working memory load. Short sentences read: The noun was adjective/verb. The nouns were either homographs or unambiguous. The adjective/verb was disambiguating for the homograph, and congruent or incongruent for the unambiguous noun. The primary noun of interest was the subordinate homograph. Comprehension of the subordinate meaning should correlate with semantic memory stores, reflecting greater knowledge. If N400 primarily reflects lexical access operations, it should also correlate with measures of semantic knowledge. If N400 reflects lexical integration, it should correlate with measures of working memory capacity. Comprehension errors were associated with semantic memory stores, but not working memory capacity. N400 was related to working memory capacity, but not semantic knowledge, suggesting that N400 primarily reflects late-stage working memory operations. N400 to subordinate disambiguating words was larger with greater working memory capacity, and thus may index the absolute capacity of working memory rather than difficulty in contextual integration.     

Specificity of memory representations for spoken words

Many theories of spoken word recognition assume that lexical items are stored in memory as abstract representations. However, recent research (e.g., Goldinger, 1996) has suggested that representations of spoken words in memory are veridical exemplars that encode specific information, such as characteristics of the talker’s voice. If representations are exemplar based, effects of stimulus variation such as that arising from changes in the identity of the talker may have an effect on identification of and memory for spoken words. This prediction was examined for an implicit and explicit task (lexical decision and recognition, respectively). Comparable amounts of repetition priming in lexical decision were found for repeated words, regardless of whether the repetitions were in the same or in different voices. However, reaction times in the recognition task were faster if the repetition was in the same voice. These results suggest a role for both abstract and specific representations in models of spoken word recognition.     

The aftermath of memory retrieval for recycling visual working memory representations

We examined the aftermath of accessing and retrieving a subset of information stored in visual working memory (VWM)—namely, whether detection of a mismatch between memory and perception can impair the original memory of an item while triggering recognition-induced forgetting for the remaining, untested items. For this purpose, we devised a consecutive-change detection task wherein two successive testing probes were displayed after a single set of memory items. Across two experiments utilizing different memory-testing methods (whole vs. single probe), we observed a reliable pattern of poor performance in change detection for the second test when the first test had exhibited a color change. The impairment after a color change was evident even when the same memory item was repeatedly probed; this suggests that an attention-driven, salient visual change made it difficult to reinstate the previously remembered item. The second change detection, for memory items untested during the first change detection, was also found to be inaccurate, indicating that recognition-induced forgetting had occurred for the unprobed items in VWM. In a third experiment, we conducted a task that involved change detection plus continuous recall, wherein a memory recall task was presented after the change detection task. The analyses of the distributions of recall errors with a probabilistic mixture model revealed that the memory impairments from both visual changes and recognition-induced forgetting are explained better by the stochastic loss of memory items than by their degraded resolution. These results indicate that attention-driven visual change and recognition-induced forgetting jointly influence the “recycling” of VWM representations.     

Trees as memory representations for simple visual patterns

The form of the memory representation for visual patterns consisting of a few line segments was investigated with three tasks. One task was the reproduction of remembered patterns using pencil and paper. The order in which the subparts of those patterns were reproduced was used to make suggestions about possible memory representations for the patterns. The second task involved rating the “goodness” of subparts of the patterns. These ratings were also interpreted as reflecting the underlying representations of the patterns. In the third task, the time required to recognize that a small pattern was part of a larger remembered pattern was used as further evidence about the memory representations of the patterns. The results from all three tasks are consistent with the theory that the memory representations are tree structures. Methods for deriving and comparing tree structures are discussed.     

The processing of interlexical homographs in translation recognition and lexical decision: Support for non-selective access to bilingual memory

In three experiments we looked at the processing of interlexical homographs by Dutch-English bilinguals. In Experiment 1 we employed the translation recognition task, a task that forces the participants to activate both language systems simultaneously. In this task the processing of interlexical homographs was inhibited substantially compared to the processing of matched control words, especially when the homograph reading to be selected was the less frequent of the homograph's two readings. In Experiments 2 and 3 we used the lexical decision task: In one condition we asked the participants to categorize letter strings as words or nonwords in Dutch; in a second condition we asked them to do so in English. The makeup of the stimulus set in Experiment 2 permitted the participants to ignore the instructions and to instantiate the task in a language-neutral form-that is, to categorize the letter strings as words in either Dutch or English. Under these circumstances a small, frequency-dependent inhibitory effect for homographs was obtained, but only in condition Dutch. In Experiment 3 the participants were forced in a language-specific processing mode by the inclusion of nonwords that were in fact words in the non-target language. Large frequency-dependent inhibitory effects for homographs were now obtained in both language conditions. The combined results are interpreted as support for the view that bilingual lexical access is non-selective.     

Syllabic and phonemic representations for short-term memory of speech stimuli

An experiment is reported which uses a same-different matching paradigm in which subjects are required to indicate whether the consonants of a pair of consonant-diphthong syllables are the same or different. The question addressed is the operation of two hypothesized processes in the perception of speech sounds. The auditory level is shown to hold stimulus information for a brief period of time and be sensitive to allophonic variations within a stimulus. Moreover, matching at this level takes place by identity of the syllables rather than of the separate phoneme segments. The phonemic level is impaired when the diphthong segments of the pair leads to a contradictory match to that of the consonants of the pair, even though only the consonants are relevant to the matching decision.     

On the perceptual specificity of memory representations

The present paradigm involved manipulating the congruency of the perceptual processing during the study and test phases of a recognition memory task. During each trial, a gaze-contingent window was used to limit the stimulus display to a region either inside or outside a 10° square centred on the participant's point of gaze, constituting the Central and Peripheral viewing modes respectively. The window position changed in real time in concert with changes in gaze position. Four experiments documented better task performance when viewing modes at encoding and retrieval matched than when they mismatched (i.e., perceptual specificity effects). Viewing mode congruency effects were demonstrated with both verbal and non-verbal stimuli. The present research is motivated and discussed in terms of theoretical views proposed in the 1970s including the levels-of-processing framework and the proceduralist viewpoint. In addition, implications for current processing and multiple systems views of memory are outlined.     

On the perceptual specificity of memory representations

The present paradigm involved manipulating the congruency of the perceptual processing during the study and test phases of a recognition memory task. During each trial, a gaze-contingent window was used to limit the stimulus display to a region either inside or outside a 10 degrees square centred on the participant's point of gaze, constituting the Central and Peripheral viewing modes respectively. The window position changed in real time in concert with changes in gaze position. Four experiments documented better task performance when viewing modes at encoding and retrieval matched than when they mismatched (i.e., perceptual specificity effects). Viewing mode congruency effects were demonstrated with both verbal and non-verbal stimuli. The present research is motivated and discussed in terms of theoretical views proposed in the 1970s including the levels-of-processing framework and the proceduralist viewpoint. In addition, implications for current processing and multiple systems views of memory are outlined.     

Conjunctive bias in memory representations of logical connectivesa

The paper presents the conjunctive bias in memory-a novel phenomenon that helps to clarify representations of logical connectives. The conjunctive bias is a tendency toward more accurate recall and recognition of conjunctive forms than of forms based on other logical connectives and a tendency to recall and recognize other logical forms as if they were conjunctions. Three experiments, in which participants' memory representations associated with different logical connectives were examined, were conducted to test the conjunctive bias hypothesis. In Experiment 1, participants learned picture-proposition pairs involving either conjunctions or disjunctions and then had to recall each proposition when cued with its picture. In Experiments 2 and 3, recognition memory for conjunctions, disjunctions, and conditionals was examined with an old/new recognition procedure. The findings of these experiments provide evidence for the conjunctive bias. Furthermore, the results of Experiment 3 suggest that corjunctive bias is not simply a pragmatically caused preference for conjunctions. The discussion focuses on the implications of these findings for current theories of deductive reasoning.     

Visuospatial bootstrapping: Long-term memory representations are necessary for implicit binding of verbal and visuospatial working memory

It has recently been shown that presenting additional visuospatial information alongside to-be-remembered numbers in a digit span task enhances participants’ memory for those items. However, the mechanisms behind this visuospatial bootstrapping effect have remained unspecified. In this article, we report evidence that this effect involves an integration of information from verbal and visuospatial temporary memory with long-term-memory (LTM) representations and that the existence of a relevant LTM representation is necessary for bootstrapping to occur.     

The influence of similarity on visual working memory representations

In verbal memory, similarity between items in memory often leads to interference and impaired memory performance. The present study sought to determine whether analogous interference effects would be observed in visual working memory by varying the similarity of the to-be-remembered objects in a colour change detection task. Instead of leading to interference and impaired performance, increased similarity among the items being held in memory led to improved performance. Moreover, when two similar colours were presented along with one dissimilar colour, memory performance was better for the similar colours than for the dissimilar colour. Similarity produced better performance even when the objects were presented sequentially and even when memory for the first item in the sequence was tested. These findings show that similarity does not lead to interference between representations in visual working memory. Instead, similarity may lead to improved task performance, possibly due to increased stability or precision of the memory representations during maintenance.     

Social representations and memory: The case of AIDS

In this study evidence is given on the mechanisms subjects use to guarantee the stability of their social representations. An initial interview was held in which subjects were asked about the causes of AIDS, affected groups and modes of transmission. Their responses were found to divide into two social representations of AIDS: a conservative-blaming representation and a liberal representation. Subjects were then given technical information about AIDS. Two weeks later, the same subjects were given a free recall test and a recognition test. The results of these tests confirmed subject's tendency to select information which is congruent with their pre-existing representations, and to distort the recall of contradictory information in order to make it compatible with pre-existing representations.     

Simultaneous control of attention by multiple working memory representations

Working memory representations play a key role in controlling attention by making it possible to shift attention to task-relevant objects. Visual working memory has a capacity of three to four objects, but recent studies suggest that only one representation can guide attention at a given moment. We directly tested this proposal by monitoring eye movements while observers performed a visual search task in which they attempted to limit attention to objects drawn in two colors. When the observers were motivated to attend to one color at a time, they searched many consecutive items of one color (long run lengths) and exhibited a delay prior to switching gaze from one color to the other (switch cost). In contrast, when they were motivated to attend to both colors simultaneously, observers' gaze switched back and forth between the two colors frequently (short run lengths), with no switch cost. Thus, multiple working memory representations can concurrently guide attention.     

Processing of representations in declarative and procedural working memory

The article investigates the relation between declarative and procedural working memory (WM; Oberauer, 2009). Two experiments test the assumption that representations in the two subsystems are selected for processing in analogous ways. Participants carried out a series of decisions on memorized lists of digits. For each decision, they had to select declarative and procedural representations. Regarding declarative representations, participants selected a memory set and a digit within this set as the input to each decision. With respect to the procedural representations, they selected a task set to be applied to the selected digit and a response within that task set. We independently manipulated the number of lists and the number of tasks to be switched among (one, two, or three; Experiment 1) and preparation time for a list switch (Experiment 2). For three effects commonly observed in task-switch studies, analogues in declarative WM were found: list-switch costs, mixing costs, and residual switch costs. List- and task-switch costs were underadditive, suggesting that declarative and procedural representations are selected separately and in parallel. The findings support the hypothesis of two analogous WM subsystems.     

Processing of representations in declarative and procedural working memory

The article investigates the relation between declarative and procedural working memory (WM; Oberauer, 2009). Two experiments test the assumption that representations in the two subsystems are selected for processing in analogous ways. Participants carried out a series of decisions on memorized lists of digits. For each decision, they had to select declarative and procedural representations. Regarding declarative representations, participants selected a memory set and a digit within this set as the input to each decision. With respect to the procedural representations, they selected a task set to be applied to the selected digit and a response within that task set. We independently manipulated the number of lists and the number of tasks to be switched among (one, two, or three; Experiment 1) and preparation time for a list switch (Experiment 2). For three effects commonly observed in task-switch studies, analogues in declarative WM were found: list-switch costs, mixing costs, and residual switch costs. List- and task-switch costs were underadditive, suggesting that declarative and procedural representations are selected separately and in parallel. The findings support the hypothesis of two analogous WM subsystems.     

The number and quality of representations in working memory

Flexible-resource theories characterize working memory as a flexible resource that can store either a large number of low-quality representations or a small number of high-quality representations. In contrast, limited-item theories propose that the number of items that can be stored in working memory is strictly limited and cannot be increased by decreasing the quality of the representations. We tested these fundamentally different conceptualizations of working memory capacity by determining whether observers could trade quality for quantity in working memory when given incentives to do so. We found no evidence that observers could increase the number of representations by decreasing their quality in working memory, but observers could make such a trade-off at earlier processing stages. Our results show that the capacity limit of working memory is best characterized as a limit on the number of items that can be stored and not as a limit on a finely divisible resource that simultaneously determines the number and quality of the representations.     

Object location memory: The interplay of multiple representations

This article reports three experiments in which the representational nature of human object location memory was studied. The results show that multiple frames of reference can be used to encode the spatial relationships among objects. Depending on their dominancy, availability, and validity, these multiple representations interact to determine memory performance. Specifically, representations that are automatically encoded and extensively practiced are more dominant, and their availability improves performance when they are valid. On the other hand, when the dominant representations are available but invalid, people may have to resort to the less dominant representations. As a result, the availability of these dominant but invalid representations can actually hurt performance, due to interference. If these interfering representations are eliminated, the performance is again improved. The implications of these findings for general human spatial cognition are discussed.     

Working memory period: the endurance of mental representations.

Working memory span assesses the maximum number of items that can be remembered in the face of concurrent processing. Models of working memory differ on several dimensions, yet many rely exclusively on this span procedure for their evidence. Three experiments consider an alternative paradigm that attempts to capture the endurance limits for remembering a fixed number of items during concurrent processing. Eight-year-old children performed two versions of this working memory period measure--operation period and reading period. Period scores show healthy test-retest reliability and external validity for scholastic attainment, comparing well with span scores in these respects. In addition, period is highly correlated with span and shows similar effects of varying the order in which stimuli are presented. We conclude that the durability of representations is an important factor in both span and period.