Visual Motion Coherence Responses in Human Visual Cortex

Abstract

1AbstractRandom dot kinematograms (RDKs) have recently been used to train subjects with cortical scotomas to perform direction of motion discrimination, partially restoring visual motion perception. To study recovery of visual perception, it is important to understand how visual areas in normal subjects and subjects with cortical scotomas respond to RDK stimuli. Studies in normal subjects have shown that Blood Oxygen Level Dependent (BOLD) responses in human area hV5/MT+ increase monotonically with coherence, in general agreement with electrophysiology studies in primates. However, RDK responses in prior studies were obtained while the subject was performing fixation, not a motion discrimination condition. Furthermore, BOLD responses were gauged against a baseline condition of uniform illumination or static dots, potentially decreasing the specificity of responses for the spatial integration of local motion signals (motion coherence). Here we revisit this question starting from a baseline RDK condition of no coherence, thereby isolating the component of BOLD response due specifically to the spatial integration of local motion signals. In agreement with prior studies, we found that responses in area hV5/MT+ of healthy subjects were monotonically increasing when subjects fixated without performing a motion discrimination task. In contrast, when subjects were performing an RDK direction of motion discrimination task, responses in area hV5/MT+ remained flat, changing minimally, if at all, as a function of motion coherence. A similar pattern of responses was seen in area hV5/MT+ of subjects with dense cortical scotomas performing direction of motion discrimination for RDKs presented inside the scotoma. Passive RDK presentation within the scotoma elicited no significant hV5/MT+ responses. These observations shed further light on how visual cortex responses behave as a function of motion coherence, helping to prepare the ground for future studies using these methods to study visual system recovery after injury.

Estimating functional EEG sources using topographical templates

“…On the contrary, when using the template or the group-lasso method for the source localization, a couple of ROIs, V3A and hMT+, are clearly active throughout the presentation of the stimuli and the waveforms are very similar. V3A and hMT+ are the two areas that are commonly found to be sensitive to motion coherence (Aspell et al, 2005; Braddick et al, 2001; Händel et al, 2007; Helfrich et al, 2013; Rees et al, 2000; Rina et al, 2022) so these results demonstrate the validity of our method when used on real data. A similar waveform is also observed in V4 which is consistent with an fMRI study that showed that V4 responds to transient increments and decrements in the level of motion coherence (Costagli et al, 2014).…”

“…This indicates that the recovered activity is not due to crosstalk or leakage from V3A and hMT+. Previous studies have also reported activation of areas located on the posterior ventral surface of the occipital lobe (Braddick et al, 2001; Händel et al, 2007; Rees et al, 2000; Rina et al, 2022). Interestingly, some of them (Braddick et al, 2001; Rina et al, 2022) found that responses in early visual areas (V1/V2) decreased as coherent motion strength increased, which is the opposite of what is observed for areas hMT+ and V3A.…”

“…Previous studies have also reported activation of areas located on the posterior ventral surface of the occipital lobe (Braddick et al, 2001; Händel et al, 2007; Rees et al, 2000; Rina et al, 2022). Interestingly, some of them (Braddick et al, 2001; Rina et al, 2022) found that responses in early visual areas (V1/V2) decreased as coherent motion strength increased, which is the opposite of what is observed for areas hMT+ and V3A. The results of the template method showing inverse activity in early ventral occipital areas compared to hMT+ and V3A is thus consistent with these reports.…”

“…Performance of the template method is particularly impressive when tested on a real dataset. It retrieves brain sources in a limited set of ROIs and these ROIs correspond to the ones identified in previous reports (Aspell et al, 2005; Braddick et al, 2001; Costagli et al, 2014; Händel et al, 2007; Helfrich et al, 2013; Lim et al, 2017; Rees et al, 2000; Rina et al, 2022).…”

“…reflect changes in global motion and can be interpreted as arising from areas that can discriminate between coherent and incoherent motion (Norcia et al, 2015). Given previous fMRI and MEG results contrasting these two types of motion, we expect sources to be present in V3A and hMT+ (Aspell et al, 2005; Costagli et al, 2014; Händel et al, 2007; Helfrich et al, 2013; Lim et al, 2017; Rees et al, 2000; Rina et al, 2022).…”