Biology subjects

Coussens, S.

Publications and source records attributed to Coussens, S..

3 recordsLinked to original sources

bioRxiv2018

Temporal expectations modulate face image repetition suppression as indexed by event-related potentials

Repeated exposure to a stimulus leads to reduced responses of stimulus-selective sensory neurons, an effect known as repetition suppression or stimulus-specific adaptation. Several influential models have been proposed to explain repetition suppression within hierarchically-organised sensory systems, with each specifying different mechanisms underlying repetition effects. We manipulated temporal expectations within a face repetition experiment to test a critical prediction of the predictive coding model of repetition suppression: that repetition effects will be larger following stimuli that appear at expected times compared to stimuli that appear at unexpected times. We recorded event-related potentials from 18 participants and mapped the spatiotemporal progression of repetition effects using mass univariate analyses. We then assessed whether the magnitudes of observed face image repetition effects were influenced by temporal expectations. In each trial participants saw an adapter face, followed by a 500ms or 1000ms interstimulus interval (ISI), and then a test face, which was the same or a different face identity to the adapter. Participants expectations for whether the test face would appear after a 500ms ISI were cued by the sex of the adapter face. Our analyses revealed multiple repetition effects with distinct scalp topographies, extending until at least 800ms from stimulus onset. An early (158-203ms) repetition effect was larger for stimuli following surprising, rather than expected, 500ms ISI durations, contrary to the model predictions of the predictive coding model of repetition suppression. Later (230-609ms) repetition effects tended to be larger following expected stimulus onset times, in line with predictive coding models. Our results indicate that the relationship between repetition suppression and temporal expectation differs across the time course of the stimulus-evoked response, suggesting multiple distinct mechanisms driving repetition suppression that operate at different latencies within the visual hierarchy.\n\nHighlights- Multiple face image repetition effects identified from 162-800ms post stimulus onset\n\n- Temporal expectations influenced the magnitudes of repetition effects\n\n- Temporal expectation effects differed for early and late stimulus-evoked responses

neuroscience↗

bioRxiv2017

Alpha Oscillatory Activity Prior to Encoding Modulates Memory Consolidation during Wake but not Sleep

Sleep promotes memory consolidation through unique neuromodulatory activity. However, little is known about the impact of attention during pre-sleep memory encoding on later memory performance. The current study aimed to address the question of whether attentional state prior to encoding, as indexed by alpha oscillatory activity, modulates the consolidation of images across periods of sleep and wake. 22 participants aged 18 - 41 years (mean age = 27.3) viewed 120 emotionally valenced images (positive, negative, neutral) before a 2hr afternoon sleep opportunity and an equivalent period of wake. Following the sleep and wake conditions, participants were required to distinguish between 120 previously seen (target) images and 120 new (distractor) images. Relative alpha power - adjusted according to participants individual alpha frequency - was computed to index attentional state prior to the learning phase. Generalised linear mixed-effects modelling revealed memory performance was modulated by attention, such that greater pre-encoding alpha power preferentially promoted memory consolidation during wake compared to sleep. There was no difference in memory performance between positive, negative and neutral stimuli. Modulations in alpha oscillatory activity may help to coordinate the flow of information between task-relevant cortical regions and a thalamo-cortical loop that preferentially subserves the formation of memory during times of wake relative to sleep.

neuroscience↗

bioRxiv2017

Perceptual Expectations Do Not Modulate Image Repetition Effects As Measured By Event-Related Potentials

Repeated stimulus presentation leads to complex changes in cortical neuron response properties, commonly known as repetition suppression or stimulus-specific adaptation. Circuit-based models of repetition suppression provide a framework for investigating patterns of repetition effects that propagate through cortical hierarchies. To further develop such models it is critical to determine whether (and if so, when) repetition effects are modulated by top-down influences, such as those related to perceptual expectation. We investigated this by presenting pairs of repeated and alternating face images, and orthogonally manipulating expectations regarding the likelihood of stimulus repetition. Event-related potentials (ERPs) were recorded from n=39 healthy adults, to map the spatiotemporal progression of stimulus repetition and expectation effects, and interactions between these factors, using mass univariate analyses. We also tested whether the ability to predict unrepeated (compared to repeated) face identities could influence the magnitude of observed repetition effects, by presenting separate blocks with predictable and unpredictable alternating faces. Multiple repetition and expectation effects were identified between 99-800ms from stimulus onset, which did not statistically interact at any point. Repetition effects in blocks with predictable alternating faces were smaller than in unpredictable alternating face blocks between 117-179ms and 506-652ms, and larger between 246-428ms. ERP repetition effects appear not to be modulated by perceptual expectations, supporting separate mechanisms for repetition and expectation suppression. However, previous studies that aimed to test for repetition effects, in which the repeated (but not unrepeated) stimulus was predictable, are likely to have conflated repetition and stimulus predictability effects.\n\nHighlights- ERP face image repetition effects were apparent between 99-800ms from stimulus onset\n- Expectations of stimulus image properties did not modulate face repetition effects\n- The predictability of unrepeated stimuli influenced repetition effect magnitudes

neuroscience↗