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 electroencephalography 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 (<80 ms post-stimulus), as indexed by the amplitude of the C1 event-related potential 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.

Influential theories propose that sensory predictions based on regularities in the environment influence information processing across the cortical hierarchy, and that attention may regulate these effects. At present, it is unclear if predictions can modulate the first feedforward sweep of visual information processing, and how this depends on attention. To address this outstanding issue, we orthogonally manipulated visuospatial predictions and attention, and used EEG and a design optimized to measure activity generated by primary visual cortex. Evidence was only found for later (>80ms) top-down modulation of cortical activity. These results have important theoretical implications in that they suggest, together with previous attention studies, that the very first stage of cortical visual information processing may generally be impenetrable to top-down influences.2009). Crucially, as prediction and attention may have opposite effects on sensory processing, with predictions reducing sensory responses and attention boosting sensory responses, their effects on visual processing may cancel out when not properly controlled for in experimental designs, potentially explaining the absence of C1 modulations in previous studies. Thus, at present, it is unclear whether predictions and attention can modulate the first feedforward sweep of cortical visual information processing, and if so, how.Here, we orthogonally manipulated prediction (stimulus location predictability) and attention (relevance), and exploited the high temporal resolution of EEG, to test this issue. Next to examining modulations of the C1, we used multivariate pattern analysis (MVPA) to further investigate how early prediction and attention may modulate visual representations. Lastly, we also explored their effects on pre-stimulus activity, indicative of a top-down bias, and on several later ERP components that capture subsequent processing stages.

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