Optokinetic nystagmus reflects perceptual directions in the onset binocular rivalry in Parkinson’s disease

Abstract

Optokinetic nystagmus (OKN), the reflexive eye movements evoked by a moving field, has recently gained interest among researchers as a useful tool to assess conscious perception. When conscious perception and stimulus are dissociated, such as in binocular rivalry—when dissimilar images are simultaneously presented to each eye and perception alternates between the two images over time—OKN correlates with perception rather than with the physical direction of the moving field. While this relationship is well established in healthy subjects, it is yet unclear whether it also generalizes to clinical populations, for example, patients with Parkinson’s disease. Parkinson’s disease is a motor disorder, causing tremor, slow movements and rigidity. It may also be associated with oculomotor deficits, such as impaired saccades and smooth pursuit eye movements. Here, we employed short-duration, onset binocular rivalry (2 s trial of stimulus presentation followed by 1 s inter-trial interval) with moving grating stimuli to assess OKN in Parkinson’s disease patients (N = 39) and controls (N = 29) of a similar age. Each trial was either non-rivalrous (same stimuli presented to both eyes) or rivalrous, as in binocular rivalry. We analyzed OKN to discriminate direction of stimulus and perception on a trial-by-trial basis. Although the speed of slow-phase OKN was slower in the patients, discriminability of conscious perception based on OKN was comparable between the groups. Treatment with anti-Parkinson drugs and deep brain stimulation improved motor ability of patients, but did not impact on OKN. Furthermore, OKN-based measures were robust and their latencies were shorter than manual button-based measures in both groups and stimulus conditions. To our knowledge, our study is the first to demonstrate that OKN can be used as a reliable indicator of conscious perception in binocular rivalry even in Parkinson’s disease patients in whom impaired manual dexterity may render button-press reports less reliable.

Deep Brain Stimulation for Parkinson’s disease changes perception in the Rubber Hand Illusion

“…This is also consistent with our study in (onset) binocular rivalry in which DBS, but not dopaminergic drugs, facilitated perceptual decisions. 38 Moreover, this facilitation effect was seen in perceptual decisions during complex binocular rivalry, but not in simpler non-rivalrous situations. 38 The STN is hypothesised to act as a brake in the cortical-striatal network, increasing the threshold of evidence required to make a complex decision when there are conflicting cuesa process thought to be disrupted by STN-DBS.…”

“…38 Moreover, this facilitation effect was seen in perceptual decisions during complex binocular rivalry, but not in simpler non-rivalrous situations. 38 The STN is hypothesised to act as a brake in the cortical-striatal network, increasing the threshold of evidence required to make a complex decision when there are conflicting cuesa process thought to be disrupted by STN-DBS. 15 How STN-DBS does this is not fully understood.…”

Perceptual reversals in binocular rivalry: Improved detection from OKN

“…As horizontal smooth pursuit tends to follow perceived horizontal motion (Enoksson, 1963;Merrill and Stark, 1963;Fujiwara et al, 2017;Frässle et al, 2014), we inferred perceived motion from horizontal velocity of smooth eye movements. In principle, zerocrossings of horizontal eye velocity may indicate reversals of perceived motion.…”

“…Typically, the recorded eye velocity is processed and filtered to extract the slow ('pursuit') phase of OKN (Naber et al, 2011;Frässle et al, 2014;Fujiwara et al, 2017) and slow velocity is categorized in a binary fashion, such as to identify periods with a consistent direction of perceived motion ('dominance periods'). While this approach reliably identifies long dominance periods, shorter periods of either dominance or transition are more difficult to resolve.…”

Measuring graded changes in consciousness through multi-target filling-in

“…Due to variations in the frequency and duration of PFI per participant, averaging data over participants is not straightforward. To resolve this, we performed image-based event-by-event analyses (Fujiwara et al, 2017) to investigate whether the amount of PFI reported may reflect changes in log(SNR). Within each participant, all PFI events were sorted in descending order based on the sum of buttons pressed at each time point, and over a 2.5 second time window (detailed below) per disappearance/reappearance event.…”