Dynamics of the straight-ahead preference in human visual cortex

Abstract

The objects located straight-ahead of the body are preferentially processed by the visual system. They are more rapidly detected and evoke stronger BOLD responses in early visual areas than elements that are retinotopically identical but located at eccentric spatial positions. To characterize the dynamics of the underlying neural mechanisms, we recorded in 29 subjects the EEG responses to peripheral targets differing solely by their locations with respect to the body. Straight-ahead stimuli led to stronger responses than eccentric stimuli for several components whose latencies ranged between 70 and 350 ms after stimulus onset. The earliest effects were found at 70 ms for a component that originates from occipital areas, the contralateral P1. To determine whether the straight-ahead direction affects primary visual cortex responses, we performed an additional experiment (n = 29) specifically designed to generate two robust components, the C1 and C2, whose cortical origins are constrained within areas V1, V2 and V3. Our analyses confirmed all the results of the first experiment and also revealed that the C2 amplitude between 130 and 160 ms after stimulus onset was significantly stronger for straight-ahead stimuli. A frequency analysis of the pre-stimulus baseline revealed that gaze-driven alterations in the visual hemi-field containing the straight-ahead direction were associated with a decrease in alpha power in the contralateral hemisphere, suggesting the implication of specific neural modulations before stimulus onset. Altogether, our EEG data demonstrate that preferential responses to the straight-ahead direction can be detected in the visual cortex as early as about 70 ms after stimulus onset.

An egocentric straight-ahead bias in primate’s vision

“…Whatever the feedforward or feedback nature of the propagation of the straight-ahead preference, this phenomenon can be considered as a mechanism of spatial attention: it serves allocating more neuronal resources for the visual analysis of a behaviourally relevant portion of the surrounding space. In line with this idea, the neural gain increases measured for straight-ahead stimuli in primary visual cortex (Strappini et al 2015) and at early latencies (Bogdanova et al 2020) are similar to those observed when manipulating attention (see, e.g., Kastner et al 1999or Liu et al 2005 for fMRI studies and Hillyard and Anllo-Vento 1998 for EEG findings). Classically, spatial attention mechanisms fall into one of 2 classes.…”

“…Altogether, these two studies demonstrated that straight-ahead effects are also observable in the human occipital cortex (notably in area V1, Strappini et al 2015 ) as early as 65–70 ms after stimulus onset (Bogdanova et al 2020 ). If these results are generally compatible with those observed in monkey electrophysiology, (Durand et al 2010 , see Sect. "…”

“…The GFPs of the differential ERPs for straightahead (orange) and eccentric (pale green) only differ around 130 ms after stimulus onset but not for the C1 component (see the first peak at t = 75 ms)(lower-right panel). Figure adapted from Bogdanova et al (2020) specific spatial positions (e.g., the straight-ahead direction) were systematically associated with gain increases.…”

“…If the spatial resolution of fMRI is good enough to determine that straight-ahead effects occur in early visual areas, and notably in V1 (Strappini et al 2015 ), its temporal resolution remains too poor to capture the dynamics of the underlying mechanisms. To characterize these dynamics, Bogdanova et al ( 2020 ) performed EEG recordings in human participants. Their stimulus was a flickering checkerboard wedge at high contrast that was presented along the horizontal meridian (i.e., at eye level) at 10° of eccentricity either to the left or to the right of ocular fixation.…”

“…To determine the first occurence of these straight-ahead effects in their data, Bogdanova et al ( 2020 ) subsequently computed the difference between EEG responses evoked by stimulations in the left and right visual hemi-fields. This operation permits to highlight another ERP component, the P1 contralateral, which peaks around 80 ms after stimulus onset (see Fig.…”