Biology subjects

Ahissar, M.

Publications and source records attributed to Ahissar, M..

9 recordsLinked to original sources

bioRxiv2024

Reduced monitoring of task performance is an effective biomarker of autism

Can reduced flexibility in autistics behavior be a reliable classifier of autism? We asked this question in the context of pitch discrimination, which is performed with similar accuracy by autistic and non-autistic participants, matched for cognitive skills. We found that three reliable, uncorrelated characteristics quantified reduced behavioral flexibility. Most non-autistic participants showed a clear feedback-related negativity (FRN) in their EEG when incorrect, larger EEG responses during feedback following difficult versus easy trials, and increased perceptual bias following correct and easy trials versus difficult ones. All three measures were weaker in autistic participants. To assess reliability, we replicated all three measures in an experiment approximately a year later. These measures were not correlated within participants, indicating that several mechanisms, associated with anterior cingulate cortex, are atypical in autism. Together, these three measures provide group classification with above 80% accuracy, showing promise for their utility as a neurocognitive biomarker of autism. Significance statementA characteristic of autism is cognitive "slowness" in updating expectations in new contexts. Our study shows that this cognitive difference is related to a reduced use of feedback, linked to atypical activity in a brain area involved in error detection and behavioral adjustment. Using EEG, we found that autistic individuals have weaker feedback-related signals and do not adjust their behavior as effectively as non-autistic individuals. Together, these neurocognitive signals could serve as a biomarker for autism. This is the first time such brain responses have been measured in a perceptual task requiring continuous adjustments. Understanding these brain mechanisms can inform strategies to enhance learning and adaptability in autism, providing new insights into the neural basis of behavioral flexibility.

neuroscience↗

bioRxiv2023

Early frequency-specific contributions to serial-effects in audition

Recent stimuli affect the perception of current stimuli, referred to as serial effects. These effects were mainly studied in the visual modality, where it was suggested that perceptual biases towards previous stimuli (contraction) stems from high-level processing stages, and promotes object-level stability. We now asked whether high object-level stages underlie contraction also in the auditory modality. We administered a two-tone pitch discrimination task using both pure and complex tones. Both have pitch, but they are perceived as different timbre categories. Pitch contraction was observed to be largest between tones of the same timbre-category, in line with the object-level account. To decipher the role of early, frequency-specific, category-indifferent processing-stages we used complex tones with missing fundamental. They differ in their low-level frequency components yet have the same pitch. Hence, a high-level account predicts that pitch contraction will remain. Surprisingly, we observed no contraction to the missing fundamental frequency. Rather, pitch was contracted to the physically-present frequencies. Supporting the low-level contribution, we found that though attention enhances contraction, it is not necessary. These observations suggest that contraction bias is an inherent part of the various stages of the auditory hierarchy of sensory processing.

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bioRxiv2022

Neural Correlates of Statistical Learning in Developmental Dyslexia: An Electroencephalography Study

The human brain extracts statistical regularities from the surrounding environment in a process referred to as statistical learning. Recent behavioural evidence suggests that developmental dyslexia affects statistical learning. However, surprisingly few neurophysiological studies have assessed how developmental dyslexia affects the neural processing underlying statistical learning. In this study, we used electroencephalography to explore the neural correlates of an important aspect of statistical learning - sensitivity to transitional probabilities - in individuals with developmental dyslexia. Adults diagnosed with developmental dyslexia (n = 17) and controls (n = 19) were exposed to a continuous stream of sound triplets in which a few triplet endings were location deviants (i.e., were presented from an unexpected speaker direction) or statistical deviants (i.e., had a low transitional probability given the triplets first two sounds). Location deviants elicited a large location mismatch negativity (MMN), which was larger in controls than dyslexics. Statistical deviants elicited a small, yet significant statistical MMN (sMMN) in controls, whereas the dyslexic individuals did not exhibit a statistical MMN. These results suggest that the neural mechanisms underlying statistical learning are impaired in developmental dyslexia. Significance statementWe assessed the neural correlates of statistical learning in individuals with developmental dyslexia. Statistical deviants, namely word endings with a low transitional probability (as compared to high probability transitions) elicited a small, yet significant statistical MMN in controls, whereas the dyslexic individuals did not exhibit a statistical MMN. Location deviants elicited a MMN, which was larger in controls than dyslexics. These results suggest that the neural mechanisms underlying statistical learning are impaired in developmental dyslexia.

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bioRxiv2020

Impaired online error-correction disrupts synchronization to external events in autism

Autism is a developmental disorder characterized by impaired social skills and accompanied by motor and perceptual atypicalities. Its etiology is an open question, partly due to the diverse range of associated difficulties. Based on recent observations that individuals with autism are slow in updating perceptual priors, we now hypothesized that motor updating is also slow. Slow motor updating is expected to hamper the ability to synchronize to external events, since asynchronies are corrected sluggishly. Since sensorimotor synchronization is important for social bonding and cooperation, its impairment is expected to impair social skills. To test this hypothesis, we measured paced finger tapping to a metronome in neurotypical, ASD, and dyslexia groups. Dyslexia was assessed as a control group with a non-social neurodevelopmental atypicality. Only the ASD group showed reduced sensorimotor synchronization. Trial-by-trial computational modelling revealed that their ability to form controlled motor responses and to maintain reliable temporal representations was adequate. Only their rate of error-correction was slow and was correlated with the severity of their social difficulties. Taken together, these findings suggest that slow updating in autism contributes to both sloppy sensorimotor performance and difficulties in forming social bonds. SignificanceThe prevalence of autism diagnosis has increased immensely is the last decades. Yet its etiology remains a challenge, partly since the functional relations between characteristic social difficulties, perceptual and motor atypicalities are not understood. Using trial-by-trial computational modelling, we show that a single deficit underlies the poor synchronization of individuals with autism in both static and changing environments. Slow updating, leading to slow online error correction of motor plans, has an immense explanatory power explaining both difficulties in sensorimotor synchronization, and social impairments.

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bioRxiv2020

Training-induced improvement in working memory tasks results from switching to efficient strategies

It is debated whether training with a working memory (WM) task, particularly n-back, can improve general WM and reasoning skills. Most training studies found substantial improvement in the trained task, with little to no transfer to untrained tasks. We hypothesized that training does not increase WM capacity, but instead provides opportunities to develop an efficient task-specific strategy. We derived a strategy for the task that optimizes WM resources and taught it to participants. In two sessions, 14 participants who were taught this strategy performed as well as 14 participants who had trained for forty sessions without strategy instructions. To understand the mechanisms underlying the no-instruction groups improvement, participants answered questionnaires during their training period. Their replies show that successful learners discovered the same strategy and improvement was associated with this discovery. We conclude that n-back training allows the discovery of strategies that enable better performance with the same WM resources.

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bioRxiv2020

Capacity of short-term memory in dyslexia is reduced due to less efficient utilization of items' long-term frequency

Dyslexia, defined as a specific impairment in decoding the written script, is the most widespread learning difficulty. However, individuals with dyslexia (IDDs) also consistently manifest reduced short-term memory (STM) capacity, typically measured by Digit Span or non-word repetition tasks. In this paper we report two experiments which test the effect of item frequency and the effect of a repeated sequence on the performance in STM tasks in good readers and in IDDs. IDDs performance benefited less from item frequency, revealing poor use of long-term single item statistics. This pattern suggests that the amply reported shorter verbal spans in dyslexia may in fact reflect their impaired sensitivity to items long-term frequency. For repeated sequence learning, we found no significant deficit among IDDs, even when a sensitive paradigm and a robust measure were used.

neuroscience↗

bioRxiv2019

Spans attributed to short-term memory are explained by sensitivity to long-term statistics in both musicians and individuals with dyslexia

Reduced short-term memory (STM) of individuals with dyslexia (IDDs) and enhanced STM of musicians are well documented, yet their causes are disputed. We hypothesized that their STMs reflect their sensitivities to accumulative long-term stimuli statistics. Indeed, when performing an STM task, IDDs had reduced benefit from syllable frequency, whereas musicians manifested an opposite effect, compared to controls. Interestingly, benefit from sequence-repetition did not significantly differ between groups, suggesting that it relies on different mechanisms. To test the generality of this separation across populations, we recruited a group of good-readers, whose native language contains a smaller fraction of the high-frequency syllables. Their span for these \"high-frequency\" syllables was small, yet their benefit from sequence-repetition was adequate. These experiments indicate that sensitivity to long-term stimuli distribution, and not to sequential repetition, is reduced in IDDs and enhanced in musicians, and this accounts for differences in their STM performance.

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bioRxiv2017

Widespread shorter cortical adaptation in dyslexia

Studies of dyslexics performance on perceptual tasks suggest that their implicit inference of sound statistics is impaired. In a previous paper (Jaffe-Dax, Frenkel, & Ahissar, 2017), using 2-tone frequency discrimination, we found that the effect of previous trial frequencies on dyslexics judgments decayed faster than the effect on controls judgments, and that the adaptation of their ERP responses to tones recovered faster. Here, we show the cortical distribution of this abnormal dynamics of adaptation using fast acquisition fMRI. We find that dyslexics faster decay of adaptation is widespread, though the most significant effects are found in the left superior temporal lobe, including the auditory cortex. This broad distribution suggests that dyslexics faster decay of implicit memory is a general characteristic of their cortical dynamics, which also encompasses the sensory cortices.

neuroscience↗

bioRxiv2016

Shorter neural adaptation to sounds accounts for dyslexics’ abnormal perceptual and reading dynamics

Dyslexia is a prevalent reading disability whose underlying mechanisms are still disputed. We studied the neural mechanisms underlying dyslexia using a simple frequency-discrimination task. Though participants were asked to compare the 2-tones in each trial, implicit memory of previous trials affected their responses. We hypothesized that implicit memory decays faster among dyslexics. We tested this by increasing the temporal intervals between consecutive trials, and measuring the behavioral impact and ERP responses from the auditory cortex. Dyslexics showed a faster decay of implicit memory effects on both measures, with similar time constants. Finally, faster decay also characterized dyslexics benefits in oral reading rate. It decreased faster as a function of the time interval from the previous reading of the same non-word. We propose that dyslexics shorter neural adaptation paradoxically accounts for their longer reading times, since it induces noisier and less reliable predictions for both simple and complex stimuli.

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