Factors influencing infants’ ability to update object representations in memory

Remembering persisting objects over occlusion is critical to representing a stable environment. Infants remember hidden objects at multiple locations and can update their representation of a hidden array when an object is added or subtracted. However, the factors influencing these updating abilities have received little systematic exploration. Here we examined the flexibility of infants’ ability to update object representations. We tested 11-month-olds in a looking-time task in which objects were added to or subtracted from two hidden arrays. Across five experiments, infants successfully updated their representations of hidden arrays when the updating occurred successively at one array before beginning at the other. But when updating required alternating between two arrays, infants failed. However, simply connecting the two arrays with a thin strip of foam-core led infants to succeed. Our results suggest that infants’ construal of an event strongly affects their ability to update memory representations of hidden objects. When construing an event as containing multiple updates to the same array, infants succeed, but when construing the event as requiring the revisiting and updating of previously attended arrays, infants fail.     

Verbal cues flexibly transform spatial representations in human memory

ABSTRACT

Humans possess a unique ability to communicate spatially-relevant information, yet the intersection between language and navigation remains largely unexplored. One possibility is that verbal cues accentuate heuristics useful for coding spatial layouts, yet this idea remains largely untested. We test the idea that verbal cues flexibly accentuate the coding of heuristics to remember spatial layouts via spatial boundaries or landmarks. The alternative hypothesis instead conceives of encoding during navigation as a step-wise process involving binding lower-level features, and thus subsequently formed spatial representations should not be modified by verbal cues. Across three experiments, we found that verbal cues significantly affected pointing error patterns at axes that were aligned with the verbally cued heuristic, suggesting that verbal cues influenced the heuristics employed to remember object positions. Further analyses suggested evidence for a hybrid model, in which boundaries were encoded more obligatorily than landmarks, but both were accessed flexibly with verbal instruction. These findings could not be accounted for by a tendency to spend more time facing the instructed component during navigation, ruling out an attentional-encoding mechanism. Our findings argue that verbal cues influence the heuristics employed to code environments, suggesting a mechanism for how humans use language to communicate navigationally-relevant information.     

Conceptual implicit memory and environmental context

Changes in environmental context between encoding and retrieval often affect explicit memory but research on implicit memory is equivocal. One proposal is that conceptual but not perceptual priming is influenced by context manipulations. However, findings with conceptual priming may be compromised by explicit contamination. The present study examined the effects of environmental context on conceptual explicit (category-cued recall) and implicit memory (category production). Explicit recall was reduced by context change. The implicit test results depended on test awareness (assessed with a post-test questionnaire). Among test-unaware participants, priming was equivalent for same-context and different-context groups, whereas for the test-aware, the same-context group produced more priming. Thus, when explicit contamination is controlled, changes in environmental context do not impair conceptual priming. Context dependency appears to be a general difference between implicit and explicit memory rather than a difference between conceptual and perceptual implicit memory. Finally, measures of mood indicated no changes in affect across contexts, arguing against mood mediation for the context effects in explicit recall.     

Interacting with objects compresses environmental representations in spatial memory

People perceive individual objects as being closer when they have the ability to interact with the objects than when they do not. We asked how interaction with multiple objects impacts representations of the environment. Participants studied multiple-object layouts, by manually exploring or simply observing each object, and then drew a scaled version of the environment (Exp. 1) or reconstructed a copy of the environment and its boundaries (Exp. 2) from memory. The participants who interacted with multiple objects remembered these objects as being closer together and reconstructed smaller environment boundaries than did the participants who looked without touching. These findings provide evidence that action-based perceptual distortions endure in memory over a moving observer’s multiple interactions, compressing not only representations between touched objects, but also untouched environmental boundaries.     

The basolateral amygdala modulates specific sensory memory representations in the cerebral cortex

Stress hormones released by an experience can modulate memory strength via the basolateral amygdala, which in turn acts on sites of memory storage such as the cerebral cortex [McGaugh, J. L. (2004). The amygdala modulates the consolidation of memories of emotionally arousing experiences. Annual Review of Neuroscience, 27, 1–28]. Stimuli that acquire behavioral importance gain increased representation in the cortex. For example, learning shifts the tuning of neurons in the primary auditory cortex (A1) to the frequency of a conditioned stimulus (CS), and the greater the level of CS importance, the larger the area of representational gain [Weinberger, N. M. (2007). Associative representational plasticity in the auditory cortex: A synthesis of two disciplines. Learning & Memory, 14(1–2), 1–16]. The two lines of research suggest that BLA strengthening of memory might be accomplished in part by increasing the representation of an environmental stimulus. The present study investigated whether stimulation of the BLA can affect cortical memory representations. In male Sprague–Dawley rats studied under urethane general anesthesia, frequency receptive fields were obtained from A1 before and up to 75 min after the pairing of a tone with BLA stimulation (BLAstm: 100 trials, 400 ms, 100 Hz, 400 μA [±16.54]). Tone started before and continued after BLAstm. Group BLA/1.0 (n = 16) had a 1 s CS–BLAstm interval while Group BLA/1.6 (n = 5) has a 1.6 s interval. The BLA/1.0 group did develop specific tuning shifts toward and to the CS, which could change frequency tuning by as much as two octaves. Moreover, its shifts increased over time and were enduring, lasting 75 min. However, group BLA/1.6 did not develop tuning shifts, indicating that precise CS–BLAstm timing is important in the anesthetized animal. Further, training in the BLA/1.0 paradigm but stimulating outside of the BLA did not produce tuning shifts. These findings demonstrate that the BLA is capable of exerting highly specific, enduring, learning-related modifications of stimulus representation in the cerebral cortex. These findings suggest that the ability of the BLA to alter specific cortical representations may underlie, at least in part, the modulatory influence of BLA activity on strengthening long-term memory.     

Interactions between visual working memory representations

We investigated whether the representations of different objects are maintained independently in working memory or interact with each other. Observers were shown two sequentially presented orientations and required to reproduce each orientation after a delay. The sequential presentation minimized perceptual interactions so that we could isolate interactions between memory representations per se. We found that similar orientations were repelled from each other whereas dissimilar orientations were attracted to each other. In addition, when one of the items was given greater attentional priority by means of a cue, the representation of the high-priority item was not influenced very much by the orientation of the low-priority item, but the representation of the low-priority item was strongly influenced by the orientation of the high-priority item. This indicates that attention modulates the interactions between working memory representations. In addition, errors in the reported orientations of the two objects were positively correlated under some conditions, suggesting that representations of distinct objects may become grouped together in memory. Together, these results demonstrate that working-memory representations are not independent but instead interact with each other in a manner that depends on attentional priority.     

The construction of large number representations in adults

What is the nature of our mental representation of quantity? We find that human adults show no performance cost of comparing numerosities across vs. within visual and auditory stimulus sets, or across vs. within simultaneous and sequential sets. In addition, reaction time and performance in such tasks are determined by the ratio of the numerosities to be compared; absolute set size has no effect. These findings suggest that modality-specific stimulus properties undergo a non-iterative transformation into representations of quantity that are independent of the modality or format of the stimulus.     

Multisensory spatial representations in eye-centered coordinates for reaching

Humans can reach for objects with their hands whether the objects are seen, heard or touched. Thus, the position of objects is recoded in a joint-centered frame of reference regardless of the sensory modality involved. Our study indicates that this frame of reference is not the only one shared across sensory modalities. The location of reaching targets is also encoded in eye-centered coordinates, whether the targets are visual, auditory, proprioceptive or imaginary. Furthermore, the remembered eye-centered location is updated after each eye and head movement. This is quite surprising since, in principle, a reaching motor command can be computed from any non-visual modality without ever recovering the eye-centered location of the stimulus. This finding may reflect the predominant role of vision in human spatial perception.     

Attachment representations in mothers of preterm infants

The aim of the study was to assess attachment representations in mothers of preterm infants using the Working Model of Child Interview (WMCI) at the 12 months of the infant's corrected age. In addition, the relation between WMCI representation categories and the Edinburgh Postnatal Depression Scale score at 6 months of the infant's corrected age was studied. There were 38 mothers of preterm infants (<1500 g or <32 gestational weeks) and 45 mothers of full-term infants. The results showed no differences between the study groups in the distribution of the three main representation categories (balanced, disengaged and distorted). However, there were qualitative differences in representations between the groups. Furthermore, maternal depression symptoms were associated with distorted representation category. We suggest that despite the qualitative differences in the mothers’ representations, mothers of preterm infants are as likely to form balanced attachments with their infants as mothers of full-term infants.     

Mental representations of social status

How do people think about social status? We investigated the nature of social status and number representations using a semantic distance latency test. In Study 1, 21 college students compared words connoting different social status as well as numbers, which served as a control task. Participants were faster at comparing occupations and numbers that were semantically farther apart relative to those more closely related. In Study 2, we examined the semantic distance effect for a social status category, for which participants have as much knowledge of, as with numbers. We asked 15 US Navy Midshipmen to compare the social status associated with different ranks in the Navy as well as compare number magnitudes. Participants were fastest when comparing ranks far in status relative to ranks close in status. These findings reveal that humans have mental representations of social status that share properties with that of number.     

Working memory selection and competition between target and distractor representations

A working memory selection task combining directed-forgetting and memory-scanning paradigms was used to test the hypothesis that difficulty in selecting target from distractor items in working memory depends on the competition between target and distractor representations, as is commonly assumed in perceptual selection research. Participants memorized two trigrams and were then cued to select one as the new memory set and forget the other. They later saw a test letter and made judgment as to whether the letter was in the selected trigram, i.e., the new memory set. Selection difficulty was examined by manipulating the type of selection cues and the time the cue could be utilized. While re-presenting the targets in the cue display facilitated selection, re-presenting distractors did not impede selection. The results suggest that working memory selection may depend more on the activation from representations of the target than of the distractor.     

Conceptual and linguistic representations of kinds and classes

We investigate the hypothesis that our conceptual systems provide two formally distinct ways of representing categories by investigating the manner in which lexical nominals (e.g., tree, picnic table) and phrasal nominals (e.g., black bird, birds that like rice) are interpreted. Four experiments found that lexical nominals may be mapped onto kind representations, whereas phrasal nominals map onto class representations but not kind representations. Experiment 1 found that phrasal nominals, unlike lexical nominals, are mapped onto categories whose members need not be of a single kind. Experiments 2 and 3 found that categories named by lexical nominals enter into both class inclusion and kind hierarchies and thus support both class inclusion (is a) and kind specification (kind of) relations, whereas phrasal nominals map onto class representations which support only class inclusion relations. Experiment 4 showed that the two types of nominals represent hierarchical relations in different ways. Phrasal nominals (e.g., white bear) are mapped onto classes that have criteria of membership in addition to those specified by the class picked out by the head noun of the phrase (e.g., bear). In contrast, lexical nominals (e.g., polar bear) specify one way to meet the criteria specified by the more general kind concept (e.g., bear). Implications for the language-conceptual system interface, representation of hierarchical relations, lexicalization, and theories of conceptual combination are discussed.     

Social representations of smoking and attitudes towards smoking restrictions in the Norwigian Navy

The present study investigated the relationship bewteen social representations about smokers and smoking, and attitudes towards smoking restrictions. Data were collected by means of questionnaires among a sample of employees ( n =4224)in the Norwegian Navy. Based on the results from first- and second-order principal components analyses, three dimensions of social representations were identified. The dimensions were labeled "negative representations", "positive representations" and "social influence". The three dimensions clearly differentiated between daliy, occasional and non-smokers. Further, structural equation modeling of the relation between social representations and attitudes towards smoking restrictions, indicated that social representations function as intermediating factors of the effect from smoking states upon attitudes towards smoking restrictions.
The findings indicate the need to focus upon social psyshological processes taking place in the ineraction between groups of smokers and non-smokers, as understanding of such processes may be relevant in preventing the development of group conflict.     

Differentiating between memory and interpretation biases in socially anxious and nonanxious individuals

Although individual cognitive biases toward threat in social anxiety are well established, few studies have examined the manner in which cognitive biases work in conjunction. In the present study, socially anxious ( n = 54 ) and nonanxious ( n = 58 ) individuals read 10 passages consisting of positive social or evaluative, negative social or evaluative, and neutral content and completed two cognitive tasks assessing memory of factual details and interpretation immediately and after 48 h. Socially anxious and nonanxious individuals did not differ in their memory for details presented in the passages. However, they made less positive and more negative interpretations of details included in the passages, particularly in positive passages that were self-relevant and particularly in positive passages after the delay. After including depression, state anxiety, and trait anxiety as covariates, biased interpretation of positive passages after the time delay remained significant, but biased interpretation of the self-relevant, positive passages did not. It is concluded that socially anxious individuals are characterized by accurate memory of threatening, factual material, but that they impose a biased interpretation upon that material, especially after some time has passed.     

Neither separate nor equivalent: Relationships between feature representations within bound objects

Evidence suggests that binding, or encoding a feature with respect to other features in time and space, can convey cognitive advantages. However, evidence across many kinds of stimuli and paradigms presents a mixed picture, alternatively showing cognitive costs or cognitive advantages associated with maintaining bound representations. We examined memory for colored letters drawn from similar and distinct color sets under circumstances that encouraged or discouraged the maintenance of color-letter binding. Our results confirmed previous change recognition research showing feature recognition improvement under explicit instructions to maintain binding. Color memory improved during binding, showing a reduced detrimental effect of feature similarity on retrieval, particularly when the letter served as the retrieval cue for a letter-color object. We found that feature recognition improved when two conditions were met: 1) relationships between features were to-be-remembered, and 2) the feature conjunction was relevant at test. Our results further suggest that this feature advantage arises because the encoded relationship between the features facilitates retrieval, not because features and objects are represented simultaneously in separate buffers.     

Meta-analysis of the association between rumination and reduced autobiographical memory specificity

The CaRFAX model, proposed by Williams J. M. G. (2006. Capture and rumination, functional avoidance, and executive control (CaRFAX): Three processes that underlie overgeneral memory. Cognition and Emotion, 20, 548–568. doi:10.1080/02699930500450465; Williams, J. M. G., Barnhofer, T., Crane, C., Herman, D., Raes, F., Watkins, E., &; Dalgleish, T. (2007). Autobiographical memory specificity and emotional disorder. Psychological Bulletin, 133(1), 122–148. doi:10.1037/0033-2909.133.1.122) posits that reduced autobiographical memory specificity, a key factor associated with the emergence and maintenance of emotional disorders, may result from heightened rumination. We provide the first meta-analysis of the relation between autobiographical memory specificity and trait rumination. PsycINFO, PsycARTICLES and MEDLINE databases were searched and the following were extracted: the correlation between the number of specific memories recalled in the Autobiographical Memory Test and self-reported trait rumination scores, and its sub-factors – brooding and reflection. The pooled effect size for the correlation between memory specificity and trait rumination was small (d?=??.05) and did not differ significantly from zero (p?=?.09). The effect sizes for the correlation with brooding and reflection were not significantly different from zero. There is limited support for the association between trait rumination and memory specificity suggested in CaRFAX.     

Infants form associations between memory representations of stimuli that are absent

Traditional models of learning assume that an association can be formed only between cues that are physically present. Here, we report that when two objects that had never appeared together were simultaneously activated in memory, young human infants associated the representations of those objects. Neither object was physically present at the time the association was formed. The association remained latent for up to 2 weeks, when the infants used it to perform a deferred imitation task. These findings reveal that what infants merely see "brings to mind" what they saw before and combines it in new ways. In addition to challenging a fundamental tenet of classic learning models, these findings have major theoretical and practical implications for early cognitive development. Every day, in the same manner, young infants probably form numerous associations between activated memories of objects that are physically absent, creating a potential knowledge base of untold dimensions.     

Judgments of associative memory

Judgments of associative memory (JAM) were indexed by ratings given to pairs of cue and response words. The normed probabilities, p(response|cue), were obtained from free association norms. The ratings were linearly related to the probabilities. The JAM functions were characterized by high intercepts ( approximately 50 on a 100 point scale) and shallow slopes (<0.5). The JAM function generalized across materials and method of rating. The function was not affected by expectancies or semantic similarity. Attempts to alter the function by making alternative responses more available were unsuccessful. A computer simulation model (MINERVA 2) exhibited the linear JAM function and successfully accounted for more complex phenomena (like the joint influence of forward and backward associative strengths on ratings). The shallow JAM slope appears to result from a fundamental lack of discrimination among associative strengths. The high intercept appears to result partly from an independent post-mnemonic source of bias producing over-estimation of association.     

Low environmental calcium blocks long-term memory formation in a freshwater pulmonate snail

The freshwater snail Lymnaea stagnalis (L.) is considered a calciphile and exhibits reduced growth and survival in environments containing less than 20 mg/l environmental calcium. Although it has no apparent effect on survival at 20 mg/l, reducing environmental calcium increases metabolic demand, and as such we consider that this level of calcium acts as a stressor on the snail. We exposed snails to acute periods of low environmental calcium and tested their ability to form intermediate-term memory (ITM) and long-term memory (LTM) following one trial operant conditioning (1TT) to reduce aerial respiratory activity in hypoxic conditions. We also assessed whether there were changes in the electrophysiological properties of a single neuron, right pedal dorsal 1 (RPeD1), which has been demonstrated to be necessary for LTM formation. Following training in high (80 mg/l) environmental calcium, L. stagnalis formed ITM and LTM lasting 24 h and demonstrated a significant reduction in all activity measured from RPeD1; however when snails were exposed to low (20 mg/l) environmental calcium they were able to form ITM but not LTM. Although no behavioral LTM was formed, a partial reduction in RPeD1 activtiy measured 24 h after training was observed, indicating a residual effect of training. The strong effect that environmental calcium concentration had on physiology and behavior in response to training to reduce aerial respiration in L. stagnalis suggests that it is an element of gastropod husbandry that needs to be carefully considered when studying other traits. This study also indicates that L. stagnalis found naturally in low calcium environments may be less able to adapt to novel stressors than populations found in harder waters.