ViSA: a neurodynamic model for visuo-spatial working memory, attentional blink, and conscious access.

Two separate lines of study have clarified the role of selectivity in conscious access to visual information. Both involve presenting multiple targets and distracters: one simultaneously in a spatially distributed fashion, the other sequentially at a single location. To understand their findings in a unified framework, we propose a neurodynamic model for Visual Selection and Awareness (ViSA). ViSA supports the view that neural representations for conscious access and visuo-spatial working memory are globally distributed and are based on recurrent interactions between perceptual and access control processors. Its flexible global workspace mechanisms enable a unitary account of a broad range of effects: It accounts for the limited storage capacity of visuo-spatial working memory, attentional cueing, and efficient selection with multi-object displays, as well as for the attentional blink and associated sparing and masking effects. In particular, the speed of consolidation for storage in visuo-spatial working memory in ViSA is not fixed but depends adaptively on the input and recurrent signaling. Slowing down of consolidation due to weak bottom-up and recurrent input as a result of brief presentation and masking leads to the attentional blink. Thus, ViSA goes beyond earlier 2-stage and neuronal global workspace accounts of conscious processing limitations.

Eyewitness memory of a supermarket robbery: a case study of accuracy and confidence after 3 months.

In this case study, 14 witnesses of an armed robbery were interviewed after 3 months. Security camera recordings were used to assess memory accuracy. Of all information that could be remembered about 84% was correct. Although accurately recalled information had a higher confidence level on average than inaccurately recalled information, the mean accuracy-confidence correlation was rather modest (0.38). These findings indicate that confidence is not a reliable predictor of accuracy. A higher level of self-reported, post-event thinking about the incident was associated with higher confidence levels, while a higher level of self-reported emotional impact was associated with greater accuracy. A potential source of (mis)information, a reconstruction of the robbery broadcasted on TV, did not alter the original memories of the witnesses.

What is learned about fragments in artificial grammar learning? A transitional probabilities approach.

Learning local regularities in sequentially structured materials is typically assumed to be based on encoding of the frequencies of these regularities. We explore the view that transitional probabilities between elements of chunks, rather than frequencies of chunks, may be the primary factor in artificial grammar learning (AGL). The transitional probability model (TPM) that we propose is argued to provide an adaptive and parsimonious strategy for encoding local regularities in order to induce sequential structure from an input set of exemplars of the grammar. In a variant of the AGL procedure, in which participants estimated the frequencies of bigrams occurring in a set of exemplars they had been exposed to previously, participants were shown to be more sensitive to local transitional probability information than to mere pattern frequencies.

Coherence and recurrency: maintenance, control and integration in working memory.

Working memory (WM), including a 'central executive', is used to guide behavior by internal goals or intentions. We suggest that WM is best described as a set of three interdependent functions which are implemented in the prefrontal cortex (PFC). These functions are maintenance, control of attention and integration. A model for the maintenance function is presented, and we will argue that this model can be extended to incorporate the other functions as well. Maintenance is the capacity to briefly maintain information in the absence of corresponding input, and even in the face of distracting information. We will argue that maintenance is based on recurrent loops between PFC and posterior parts of the brain, and probably within PFC as well. In these loops information can be held temporarily in an active form. We show that a model based on these structural ideas is capable of maintaining a limited number of neural patterns. Not the size, but the coherence of patterns (i.e., a chunking principle based on synchronous firing of interconnected cell assemblies) determines the maintenance capacity. A mechanism that optimizes coherent pattern segregation, also poses a limit to the number of assemblies (about four) that can concurrently reverberate. Top-down attentional control (in perception, action and memory retrieval) can be modelled by the modulation and re-entry of top-down information to posterior parts of the brain. Hierarchically organized modules in PFC create the possibility for information integration. We argue that large-scale multimodal integration of information creates an 'episodic buffer', and may even suffice for implementing a central executive.

Flashbulb and event memory of September 11, 2001: consistency, confidence and age effects.

We used the terrorist attacks on September 11, 2001 to investigate if the formation, confidence, and nature of flashbulb memories were dependent on age. In addition, we compared the consistency over time of flashbulb memories with event memory, i.e., widely publicized factual details of the event, in a group of young respondents. College students (n=34, M age 24.8 yr.) were questioned 2 wk. after the attack and again 2 mo. later. At the later time, also a group of healthy elderly respondents (n=20, M age 70.5 yr.) was asked the same questions. Performance of young and old participants did not differ. Flashbulb memories were found without exception for both time periods and in both age groups. These memories had high confidence ratings and were described as very vivid. The original event was judged to have been accompanied by high emotion and rehearsal. In the college group, event memory, and to a smaller extent also flashbulb memory, decreased in accuracy already over the 2 mo. We conclude that flashbulb memories are a special case of normal episodic memory for emotional events. The creation of flashbulb memories, however, requires a special scenario of emotional arousal and rehearsal.

Consistency of memory for emotionally arousing events: a review of prospective and experimental studies.

Although emotionally arousing events are more memorable than ordinary daily life events, the nature of memories for emotionally arousing events is widely debated. On the one hand, researchers consider memories for highly emotional events as malleable and subject to distortion, while on the other hand these memories are perceived as both indelible and consistent over the lifetime. Up till now, a systematic comparison of research findings on consistency of memory for emotional events is lacking. This paper is the first effort to summarize available studies on consistency of memory for emotionally arousing events and to address methodological limitations and suggestions for future research as well. In general, findings show that quality of the selected studies is sufficient to good, with studies with victims of assault and studies on war-exposure reaching higher quality scores than studies on flashbulb memories and experimental memory studies. Victims of assault or war-exposure tend to amplify their memories for the event, while results from flashbulb memory research and experimental research suggest that memory for emotional events is either stable or diminishes over time.

Interference in implicit memory caused by processing of interpolated material.

This study addresses the susceptibility of implicit memory to interference. Interference is manipulated by presenting interpolated lists of words that do or do not have word stems in common with previously studied target words (e.g., target word paragraph followed by interpolated words such as paradise or vicinity). Interference in a word stem completion task occurred only when words had similar word stems (Experiment 1). Increasing the number of interpolated words with corresponding word stems (e.g., not only paradise but also parking, pardon, and parliament) produced increasing amounts of interference (Experiment 2). Interference in implicit memory appears to be a simple response competition phenomenon that occurs when cues simultaneously activate primed targets and primed competing responses. The amount of interference can be explained by a quantitative model of the relative strengths of target and competing responses.

Evidence for two processes underlying the serial position curve of single- and multi-trial free recall in a heterogeneous group of psychiatric patients: a confirmatory factor analytic study.

The U-shaped serial position curve (SPC) of single-trial free recall is a well-established empirical fact, and there is ample evidence that it is the result of two different memory functions. However, it is insufficiently clear whether the same holds true for the SPC of multi-trial free recall. Free recall test measurements of two large heterogeneous groups of psychiatric patients were subjected to factor extraction using Principal Components Analysis and oblique rotation in two studies. The results of these two experiments show that the SPCs of single- and multi-trial free recall arise from the same two functions i.e. one function underlies the recency part, the other the primacy and middle (prerecency) part. Possible theoretical interpretations are discussed.

Blinks of the mind: memory effects of attentional processes.

If 2 words are presented successively within 500 ms, subjects often miss the 2nd word. This attentional blink reflects a limited capacity to attend to incoming information. Memory effects were studied for words that fell within an attentional blink. Unrelated words were presented in a modified rapid serial visual presentation task at varying stimulus-onset asynchronies, and attention was systematically manipulated. Subsequently, recognition, repetition priming, and semantic priming were measured separately in 3 experiments. Unidentified words showed no recognition and no repetition priming. However, blinked (i.e., unidentified) words did produce semantic priming in related words. When, for instance, ring was blinked, it was easier to subsequently identify wedding than apple. In contrast, when the blinked word itself was presented again, it was not easier to identify than an unrelated word. Possible interpretations of this paradoxical finding are discussed.