Contents lists available at ScienceDirect Brain and Cognition journal homepage: www.elsevier.com/locate/b&c Binocular rivalry after right-hemisphere stroke: Effects of attention impairment on perceptual dominance patterns Kjersti Mæhlum Walle a,b, ⁎ , Hillary Lynn Kyler a,b , Jan Egil Nordvik a , Frank Becker a,c , Bruno Laeng b a Sunnaas Rehabilitation Hospital, Nesoddtangen, Norway b Department of Psychology, University of Oslo, Oslo, Norway c Institute of Clinical Medicine, University of Oslo, Oslo, Norway ARTICLE INFO Keywords: Binocular rivalry Neglect Attention Spatial frequency Perception ABSTRACT Binocular rivalry is when perception fluctuates while the stimuli, consisting of different images presented to each eye, remain unchanged. The fluctuation rate and predominance ratio of these images are regarded as in- formation source for understanding properties of consciousness and perception. We administered a binocular rivalry task to 26 right-hemisphere stroke patients and 26 healthy control participants, using stimuli such as simple Gabor anaglyphs. Each single Gabor image was of unequal spatial frequency compared to its counterpart, allowing assessment of the effect of relative spatial frequency on rivalry predominance. Results revealed that patients had significantly decreased alternation rate compared to healthy controls, with severity of patients’ attention impairment predicting alternation rates. The patient group had higher predominance ratio for high compared to low relative spatial frequency stimuli consistent with the hypothesis that damage to the right hemisphere may disrupt processing of relatively low spatial frequencies. Degree of attention impairment also predicted the effect of relative spatial frequencies. Lastly, both groups showed increased predominance rates in the right eye compared to the left eye. This right eye dominance was more pronounced in patients than controls, suggesting that right hemisphere stroke may additionally affect eye predominance ratios. 1. Introduction Binocular rivalry is a compelling phenomenon causing fluctuations in visual awareness. Two different images are presented simulta- neously, one to each eye, resulting in conflicting information in the brain. Instead of perceiving a meaningless blend of the two images, only one image is perceived at a time, as fluctuating neural activity leads to alternating phases of suppression and dominance for each of the two percepts (Blake, 2005). Although external stimuli remain the same and the visual system is stimulated by unchanging information or visual input, the perceptual experience alters. Hence, any change in percep- tion ought to reflect fluctuation of visual consciousness. Attention processes involved during binocular rivalry have been carefully examined in the past (see Dieter & Tadin, 2011; Paffen & Alais, 2011), though uncertainty remains regarding the role of attention in conscious and unconscious processing in patients with attention defi- cits. Investigating patients with attention impairments provides an opportunity to learn more about the underlying mechanisms involved in binocular rivalry. Stroke commonly results in attention deficits, with right-hemisphere stroke more often resulting in unilateral neglect, a syndrome affecting the patient’s ability to attend to and perceive stimuli on the side of space/body contralateral to the injured hemisphere (Cherney, Halper, Kwasnica, Harvey, & Zhang, 2001; Corbetta, Kincade, Lewis, Snyder, & Sapir, 2005; Denes, Semenza, Stoppa, & Lis, 1982; Jehkonen et al., 2000). Additionally, sustained attention required during bino- cular rivalry has been associated with the right hemisphere and could thus be compromised in right-hemisphere stroke patients (Robertson, Ridgeway, Greenfield, & Parr, 1997). Damage to the attention system can cause non-spatial, or global, attention deficits (Priftis, Bonato, Zorzi, & Umilta, 2013), and these impairments might in turn alter the dynamics of perceptual processing. During binocular rivalry the conflicting scenes are in the same location in the visual field, making the paradigm ideal for investigating the ef- fects of brain damage on changes in non-spatial attention. The task allows assessment of changes in neural competition due to hemispheric injury. However, little research has been conducted on binocular rivalry in http://dx.doi.org/10.1016/j.bandc.2017.06.007 Received 26 May 2016; Received in revised form 18 May 2017; Accepted 16 June 2017 ⁎ Corresponding author at: Sunnaas Rehabilitation Hospital, Department of Research, Bjørnemyrveien 11, 1450 Nesoddtangen, Norway. E-mail address: stiprust@sunnaas.no (K.M. Walle). Brain and Cognition xxx (xxxx) xxx–xxx 0278-2626/ © 2017 Elsevier Inc. All rights reserved. Please cite this article as: Walle, K.M., Brain and Cognition (2017), http://dx.doi.org/10.1016/j.bandc.2017.06.007