Biology subjects

Slagter, H. A.

Publications and source records attributed to Slagter, H. A..

21 records · Page 2Linked to original sources

bioRxiv2018

No evidence that predictions and attention modulate the first feedforward sweep of cortical information processing

Predictive coding models propose that predictions (stimulus likelihood) reduce sensory signals as early as primary visual cortex (V1), and that attention (stimulus relevance) can modulate these effects. Indeed, both prediction and attention have been shown to modulate V1 activity, albeit with fMRI, which has low temporal resolution. This leaves it unclear whether these effects reflect a modulation of the first feedforward sweep of visual information processing and/or later, feedback-related activity. In two experiments, we used EEG and orthogonally manipulated spatial predictions and attention to address this issue. Although clear top-down biases were found, as reflected in pre-stimulus alpha-band activity, we found no evidence for top-down effects on the earliest visual cortical processing stage (<80ms post-stimulus), as indexed by the amplitude of the C1 ERP component and multivariate pattern analyses. These findings indicate that initial visual afferent activity may be impenetrable to top-down influences by spatial prediction and attention.

neuroscience↗

bioRxiv2017

Expect to neglect: Cross-modal resource allocation in anticipation of visual load

Human information processing is limited in capacity. To prevent sensory overload, expectation of upcoming events has been suggested to allocate processing resources to task-relevant regions (e.g., visual system), at the expense of processing in task-irrelevant regions (e.g., auditory system). In support of this, for tasks involving a high visual perceptual load (e.g. visual target search within physically similar distractors), auditory evoked responses were found to be attenuated1. This EEG study aimed to further elucidate the neural mechanisms by which the brain prepares for sensory overload. We investigated how expectancy about visual load modulated neural activity, prior to the onset of visual stimuli. Visual load in a letter search task was manipulated by varying the target letters similarity to the remaining letters and the letter set size from which flankers were randomly drawn. Importantly, audio-visual cues signaled the likely visual load of the upcoming stimulus-array, manipulating expectancy about visual task load. Cues signaling high visual load elicited attenuated auditory-evoked responses and increased alpha activity over task-irrelevant (auditory) regions, suggesting a functional inhibition of those regions already prior to the arrival of the visual array to suppress auditory cue processing. We also observed a sustained posterior positivity in the ERPs after high perceptual load cues, whose amplitude correlated with reaction times, suggestive of resource allocation for the upcoming visual targets. Expectation about visual load may thus prepare the attentional system both by facilitating target processing and task execution and inhibiting irrelevant sensory processing, thus providing efficient means to overcome attentional limits in situations with complex visual input.

neuroscience↗

bioRxiv2017

Dynamic interactions between top-down expectations and conscious awareness

It is well known that top-down expectations affect perceptual processes. Yet, remarkably little is known about the relationship between expectations and conscious awareness We address three crucial questions that are outstanding: 1) How do predictions affect the likelihood of conscious stimulus perception?; 2) Does the brain register violations of predictions nonconsciously?; and 3) Do predictions need to be conscious to influence perceptual decisions? We performed three experiments in which we manipulated stimulus predictability within the attentional blink paradigm, while combining visual psychophysics with electrophysiological recordings. We found that valid stimulus expectations increase the likelihood of conscious access of stimuli. Furthermore, our findings suggest a clear dissociation in the interaction between expectations and consciousness: conscious awareness seems crucial for the implementation of top-down predictions, but not for the bottom-up generation of stimulus-evoked prediction errors. These results constrain and update influential theories about the role of consciousness in the predictive brain.

neuroscience↗