Motion-induced blindness as a noisy excitable system.

Perceptual disappearance of a salient target induced by a moving texture mask (MIB: Motion-Induced Blindness) is a striking effect, currently poorly understood. Here, we investigated whether the dynamics of MIB qualify as an excitable system. Excitable systems exhibit fast switches from one state to another (e.

Forgetting dynamics for items of different categories.

How the dynamic evolution of forgetting changes for different material types is unexplored. By using a common experimental paradigm with stimuli of different types, we were able to directly cross-examine the emerging dynamics and found that even though the presentation sets differ minimally by design, the obtained curves appear to fall on a discrete spectrum. We also show that the resulting curves do not depend on physical time but rather on the number of items shown.

Effects of order on memory of event times.

Memorizing time of an event may employ two processes (1) encoding of the absolute time of events within an episode, (2) encoding of its relative order. Here we study interaction between these two processes. We performed experiments in which one or several items were presented, after which participants were asked to report the time of occurrence of items.

Changes in Cortical Coherence Supporting Complex Visual and Social Processing in Adolescence.

Despite our differences, there is much about the natural visual world that most observers perceive in common. Across adults, approximately 30% of the brain is activated in a consistent fashion while viewing naturalistic input. At what stage of development is this consistency of neural profile across individuals present? Here, we focused specifically on whether this mature profile is present in adolescence, a key developmental period that bridges childhood and adulthood, and in which new cognitive and social challenges are at play.

Retroactive interference model of forgetting.

Memory and forgetting constitute two sides of the same coin, and although the first has been extensively investigated, the latter is often overlooked. A possible approach to better understand forgetting is to develop phenomenological models that implement its putative mechanisms in the most elementary way possible, and then experimentally test the theoretical predictions of these models. One such mechanism proposed in previous studies is retrograde interference, stating that a memory can be erased due to subsequently acquired memories.

Fundamental Law of Memory Recall.

Human memory appears to be fragile and unpredictable. Free recall of random lists of words is a standard paradigm used to probe episodic memory. We proposed an associative search process that can be reduced to a deterministic walk on random graphs defined by the structure of memory representations.

Emergence of hierarchical organization in memory for random material.

Structured information is easier to remember and recall than random one. In real life, information exhibits multi-level hierarchical organization, such as clauses, sentences, episodes and narratives in language. Here we show that multi-level grouping emerges even when participants perform memory recall experiments with random sets of words.

Memory States and Transitions between Them in Attractor Neural Networks.

Human memory is capable of retrieving similar memories to a just retrieved one. This associative ability is at the base of our everyday processing of information. Current models of memory have not been able to underpin the mechanism that the brain could use in order to actively exploit similarities between memories.

Synaptic Correlates of Working Memory Capacity.

Psychological studies indicate that human ability to keep information in readily accessible working memory is limited to four items for most people. This extremely low capacity severely limits execution of many cognitive tasks, but its neuronal underpinnings remain unclear. Here we show that in the framework of synaptic theory of working memory, capacity can be analytically estimated to scale with characteristic time of short-term synaptic depression relative to synaptic current time constant.

Practice makes perfect in memory recall.

A large variability in performance is observed when participants recall briefly presented lists of words. The sources of such variability are not known. Our analysis of a large data set of free recall revealed a small fraction of participants that reached an extremely high performance, including many trials with the recall of complete lists.

Neural Network Model of Memory Retrieval.

Human memory can store large amount of information. Nevertheless, recalling is often a challenging task. In a classical free recall paradigm, where participants are asked to repeat a briefly presented list of words, people make mistakes for lists as short as 5 words.

Visual perception of order-disorder transition.

Our experience with the natural world, as composed of ordered entities, implies that perception captures relationships between image parts. For instance, regularities in the visual scene are rapidly identified by our visual system. Defining the regularities that govern perception is a basic, unresolved issue in neuroscience.

Effects of long-term representations on free recall of unrelated words.

Human memory stores vast amounts of information. Yet recalling this information is often challenging when specific cues are lacking. Here we consider an associative model of retrieval where each recalled item triggers the recall of the next item based on the similarity between their long-term neuronal representations.

Word length effect in free recall of randomly assembled word lists.

In serial recall experiments, human subjects are requested to retrieve a list of words in the same order as they were presented. In a classical study, participants were reported to recall more words from study lists composed of short words compared to lists of long words, the word length effect. The world length effect was also observed in free recall experiments, where subjects can retrieve the words in any order.

Decision criteria in dual discrimination tasks estimated using external-noise methods.

According to classical signal detection theory (SDT), in simple detection or discrimination tasks, observers use a decision parameter based on their noisy internal response to set a boundary between "yes" and "no" responses. Experimental paradigms where performance is limited by internal noise cannot be used to provide an unambiguous measure of the decision criterion and its variability. Here, unidimensional external noise is used to estimate a criterion and its variability in stimulus space.

Lateral facilitation--no effect on the target noise level.

The detection threshold of a centrally placed Gabor target is reduced in the presence of aligned high-contrast Gabor patches that are optimally spaced from the target (Polat & Sagi, 1993). Here we determined whether threshold reduction is due to signal enhancement or to decreased signal response variability (internal noise), using a recently developed analysis for a Signal Detection Theory (SDT)-based contrast-identification paradigm (Katkov, Tsodyks, & Sagi, 2007a). We found that flankers did not affect internal noise, but instead caused increased target response when collinear with it, in agreement with the lateral facilitation effect.

Inverse modeling of human contrast response.

Mathematical singularities found in the Signal Detection Theory (SDT) based analysis of the 2-Alternative-Forced-Choice (2AFC) method [Katkov, M., Tsodyks, M., & Sagi, D.

Singularities in the inverse modeling of 2AFC contrast discrimination data.

Analytical calculations show that two-alternative force-choice data are not always suitable for specifying the parameters of the underlying discrimination model. Experimentally, we show here that in the case of contrast discrimination in humans, a variety of models spanning a large range of parameters can explain the data within an experimental error. Monte-Carlo simulations indicate that the number of trials in psychophysical experiments is not the limiting factor in estimating the parameters in contrast discrimination.