Abstract
Upright perception is a key aspect of orientation constancy, as we maintain a stable perception of the world despite continuous movements of our eyes, head, and body. Torsional position of the eyes can impact perception of upright by changing orientation of the images on the retina relative to gravity. Here, we investigated the role of temporoparietal cortex in upright perception with respect to ocular torsion, by means of the inhibitory effect of continuous theta burst transcranial magnetic stimulation (TMS). We used a subjective visual vertical (SVV) paradigm to track changes in upright perception, and a custom video method to track ocular torsion simultaneously. Twelve participants were tested during a lateral head tilt of 20° to the left. TMS at the posterior aspect of the supramarginal gyrus (SMGp) resulted in an average SVV shift in the opposite direction of the head tilt compared to a sham stimulation (1.8°). Ocular torsion following TMS at SMGp showed no significant change compared to the sham stimulation (−0.1°). Thus, changes in upright perception at SMGp were dissociated from ocular torsion. This finding suggests that perception of upright at SMGp is primarily related to sensory processing for spatial orientation, as opposed to subcortical regions that have direct influence on ocular torsion.
Highlights
Human studies have shown a multisensory role of the temporoparietal cortex in perception of spatial orientation [1,2,3,4,5,6]
We accounted for baseline subjective visual vertical (SVV) and ocular torsion values to determine the effects of transcranial magnetic stimulation (TMS) and sham stimulations
SVV and ocular torsion shifts were calculated by subtracting the average pre-stimulation values from the poststimulation values, which eliminated the variable effect of head tilt across participants
Summary
Human studies have shown a multisensory role of the temporoparietal cortex in perception of spatial orientation [1,2,3,4,5,6]. Multisensory integration is vital for orientation constancy since our eye, head and body positions change frequently. Such orientation constancy allows us to inherently perceive the world in upright orientation, despite the changing position of the images on the retina. Perception of upright can be measured by a psychophysical task known as the subjective visual vertical (SVV). In this task, a visual line is used to measure the perceived earth-vertical orientation [7,8,9,10]. When the head is tilted laterally toward the shoulder, the eyes roll in the opposite direction
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