Optic-flow selective cortical sensory regions associated with self-reported states of vection

Abstract

Optic flow is one of the most important visual cues to the estimation of self-motion. It has repeatedly been demonstrated that a cortical network including visual, multisensory, and vestibular areas is implicated in processing optic flow; namely, visual areas middle temporal cortex (MT+), V6; multisensory areas ventral intra-parietal area (VIP), cingulate sulcus visual area, precuneus motion area (PcM); and vestibular areas parieto-insular vestibular cortex (PIVC) and putative area 2v (p2v). However, few studies have investigated the roles of and interaction between the optic-flow selective sensory areas within the context of self-motion perception. When visual information (i.e., optic flow) is the sole cue to computing self-motion parameters, the discrepancy amongst the sensory signals may induce an illusion of self-motion referred to as 'vection.' This study aimed to identify optic-flow selective sensory areas that are involved in the processing of visual cues to self-motion, by introducing vection as an index and assessing activation in which of those areas reflect vection, using functional magnetic resonance imaging. The results showed that activity in visual areas MT+ and V6, multisensory area VIP and vestibular area PIVC was significantly greater while participants were experiencing vection, as compared to when they were experiencing no vection, which may indicate that activation in MT+, V6, VIP, and PIVC reflects vection. The results also place VIP in a good position to integrate visual cues related to self-motion and vestibular information.

Keywords: fMRI; multisensory; optic flow; self-motion; sensory integration; vection; vestibular; visual.

FIGURE 1

Experimental procedure and stimuli. Timeline illustrates the stimuli presented during the gradient and no-gradient conditions, and a blank screen with a fixation point presented during inter-stimulus interval (ISI). During the stimulus-presentation blocks, participants held down one of the two buttons to indicate whether they were experiencing vection or no vention.

FIGURE 2

Duration of vection perceived during 16-s stimulus blocks in gradient and no-gradient conditions averaged over 10 runs for each participant. Error bars indicate SE.

FIGURE 3

Regions of interests (ROIs): Optic-flow selective sensory regions. The map of areas that showed a significantly greater response to optic-flow stimulus than to random-motion stimulus is superimposed onto inflated representations of the left and right hemispheres of one representative brain. T-values are color-coded (see color bar). All activation shown is thresholded at p < 0.005 uncorrected.

FIGURE 4

BOLD responses to optic-flow stimuli with and without speed gradient, for MT+, V6, ventral intra-parietal area (VIP), cingulate sulcus visual area (CSv), precuneus motion area (PcM), p2v, and parieto insular vestibular cortex (PIVC) in one representative brain. Time series data for the two conditions and for the two hemispheres are overlaid. A single time series was computed from 10 runs. The time series was then collapsed over a single stimulus cycle of 32 s: The stimulus-presentation block lasted from 0 to 16 s followed by a 16-s ISI. Error bars indicate SE.

FIGURE 5

BOLD responses during vection and no-vection events, for MT+, V6, VIP, CSv, PcM, p2v, and PIVC in one representative brain. Time series data for the two types of events and for the two hemispheres are overlaid. A single time series was computed from 10 runs. The time series was then collapsed over a single cycle of 32 s. Error bars indicate SE.