Role of lateral and feedback connections in primary visual cortex in the processing of spatiotemporal regularity - a TMS study.

Our human visual system exploits spatiotemporal regularity to interpret incoming visual signals. With a dynamic stimulus sequence of four collinear bars (predictors) appearing consecutively toward the fovea, followed by a target bar with varying contrasts, we have previously found that this predictable spatiotemporal stimulus structure enhances target detection performance and its underlying neural process starts in the primary visual cortex (area V1). However, the relative contribution of V1 lateral and feedback connections in the processing of spatiotemporal regularity remains unclear. In this study we measured human contrast detection of a briefly presented foveal target that was embedded in a dynamic collinear predictor-target sequence. Transcranial magnetic stimulation (TMS) was used to selectively disrupt V1 horizontal and feedback connections in the processing of predictors. The coil was positioned over a cortical location corresponding to the location of the last predictor prior to target onset. Single-pulse TMS at an intensity of 10% below phosphene thresholdwas delivered at 20 or 90ms after the predictor onset. Our analysis revealed that the delivery of TMS at both time windows equally reduced, but did not abolish, the facilitation effect of the predictors on target detection. Furthermore, if the predictors' ordination was randomized to suppress V1 lateral connections, the TMS disruption was significantly more evident at 20ms than at 90-ms time window. We suggest that both lateral and feedback connections contribute to the encoding of spatiotemporal regularity in V1. These findings develop understanding of how our visual system exploits spatiotemporal regularity to facilitate the efficiency of visual perception.

Event-related potential correlates of the interaction between attention and spatiotemporal context regularity in vision.

Visual perception is influenced at early processing stages by geometric spatiotemporal context regularities (consistent with the "vision-as-inference" view) and by attention, yet little is known about the interaction between these two influences on visual processing. Here, we investigate the temporal dynamics of the interaction between attention and spatiotemporal context regularity in target detection using event-related potentials (ERP). Spatial attention was withdrawn from the context by a secondary task in Experiment 1, and the role of task-relevance was explored in Experiment 2 by including a passive viewing condition. The ERP correlates of spatiotemporal regularity reported in an earlier study were replicated in single task (Experiment 1) and active viewing (Experiment 2): P1 and N1 peak-latency was shorter when the target was preceded by a context. Latency first differentiated between the two context conditions at N1, where latency was shortest for targets preceded by a context with both spatial and temporal regularities (compared with temporal regularity only). In dual task and passive viewing, this N1 latency-shift was abolished. Comparisons of "low-attention" (dual task or passive viewing) with "high-attention" conditions (single task or active viewing) revealed that attention only shortened N1 peak-latency when the target was preceded by stimulus sequences with spatial and temporal regularity. P1 latency was unaffected by manipulation of top-down attention factors. Attentional factors are likely to modulate influences of spatiotemporal context through re-afferent projections at later stages of visual processing in regions of extrastriate cortex associated with the generators of the N1 waveform.