Vision Research 83 (2013) 76–81 Contents lists available at SciVerse ScienceDirect Vision Research journal homepage: www.elsevier.com/locate/visres Effects of attention on visual experience during monocular rivalry ⇑ Eric A. Reavis a, , Peter J. Kohler a, Gideon P. Caplovitz b, Thalia P. Wheatley a, Peter U. Tse a a Department of Psychological & Brain Sciences, Dartmouth College, 6207 Moore Hall, Hanover, NH 03755, United States b Department of Psychology, University of Nevada at Reno, 1664 North Virginia Street, Psychology Department Mailstop 0296, Reno, NV 89557-0296, United States article info abstract Article history: There is a long-running debate over the extent to which volitional attention can modulate the appearance Received 20 November 2012 of visual stimuli. Here we use monocular rivalry between afterimages to explore the effects of attention Received in revised form 4 February 2013 on the contents of visual experience. In three experiments, we demonstrate that attended afterimages are Available online 13 March 2013 seen for longer periods, on average, than unattended afterimages. This occurs both when a feature of the afterimage is attended directly and when a frame surrounding the afterimage is attended. The results of Keywords: these experiments show that volitional attention can dramatically influence the contents of visual Visual attention experience. Monocular rivalry Ó 2013 Elsevier Ltd. All rights reserved. Consciousness Afterimages 1. Introduction Logothetis, 2002; Leopold & Logothetis, 1999). It has been shown to exhibit a characteristic distribution of dominance durations Can volitional attention alter the appearance of visual stimuli? and alternation rates that is similar to those observed in ambigu- Disagreement over this question has persisted for over a century, ous figure perception (Brascamp et al., 2005; van Ee, 2005; Zhao with, for example, Hermann von Helmholtz arguing in the affirma- et al., 2004). Based largely on the similar properties of binocular tive and Gustav Fechner in the negative (Helmholtz, 1866/1924). In rivalry and ambiguous figure perception, some have proposed that recent years, evidence has begun to accumulate in favor of the po- a single, supra-modal mechanism for resolving perceptual ambigu- sition that volitional attention can indeed alter the appearance of ity could drive the alternations in all forms of perceptual multista- visual stimuli (Abrams, Barbot, & Carrasco, 2010; Liu, Abrams, & bility (Leopold & Logothetis, 1999). If this is true, then it would Carrasco, 2009; Tse, 2005). Volitional attention can also alter the follow that manipulations which affect the alternation process in contents of visual experience by biasing perception toward a par- one form of multistability would likely have similar effects on ticular percept in binocular rivalry and ambiguous figure percep- the alternation process in other forms of multistability. tion, where visual experience alternates between several Binocular rivalry and ambiguous figure perception can both be different percepts (Chong, Tadin, & Blake, 2005; Hancock & influenced by volitional attention (Chong, Tadin, & Blake, 2005; Andrews, 2007; Meng & Tong, 2004; Ooi & He, 1999; van Ee, van Hancock & Andrews, 2007; Meng & Tong, 2004; Ooi & He, 1999; Dam, & Brouwer, 2005). Here we demonstrate for the first time van Ee, van Dam, & Brouwer, 2005). If shared mechanisms are an effect of volitional attention on another type of perceptual mul- responsible for the perceptual switching that occurs in monocular tistability: monocular rivalry. rivalry, binocular rivalry, and ambiguous figure perception, then In monocular rivalry, a single image of two spatially overlapping attention might have a similar effect on perceptual switching in transparent surfaces can lead to the experience of perceptual alter- monocular rivalry as it does in other types of multistable percep- nations between the two surfaces (Breese, 1899). Qualitatively, tion. To our knowledge, it remains an open question whether monocular rivalry resembles binocular rivalry, where different attention influences monocular rivalry (although O’Shea (2006), images presented to the two eyes alternate in visibility. Indeed, published an abstract reporting possible effects of attention on there is evidence that the alternation dynamics and suppression ef- monocular rivalry). fects which occur in monocular rivalry are similar to those of binoc- Here, we examine the influence of volitional attention on the vi- ular rivalry (Maier, Logothetis, & Leopold, 2005; O’Shea et al., 2009). sual experience of color afterimages engaged in monocular rivalry. Binocular rivalry has been characterized far more extensively Afterimages were induced by stimuli like those shown in Fig. 1. than monocular rivalry (for reviews, see Blake, 2001; Blake & Color afterimages typically occur when opponent-coded retinal ganglion cells undergo a rebound in firing following prolonged exposure to an unchanging stimulus (Zaidi et al., 2012). To the ⇑ Corresponding author. E-mail address: [email protected] (E.A. Reavis). viewer, the afterimages appear like a weak version of the color 0042-6989/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.visres.2013.03.002 E.A. Reavis et al. / Vision Research 83 (2013) 76–81 77 an outlier who, in several analyses, was more than three standard deviations from the group mean. Exclusion of the outlier did not change the direction or significance of any of the reported results. In this and subsequent experiments, all participants gave informed consent to participate, and all experimental procedures were ap- proved by the Dartmouth Committee for the Protection of Human Subjects. Participants viewed stimuli on a Mitsubishi Diamond Pro 2070SB CRT monitor from a distance of 57 cm, in a darkened room. Stimuli were generated and presented using the Psychophysics Toolbox, version 3, on a PC running MATLAB R2010a in Linux (Brainard, 1997; Pelli, 1997; MathWorks, Natick, MA). Each participant completed 100 experimental trials. On each trial, participants fixated on a dot in the center of the screen and pressed a key to initiate the trial. While fixating, they passively viewed an adapting stimulus for 10 s (example in Fig. 1a). The adapting stimulus contained two overlapping rectangular frames forming a plus-sign (12 Â 12 deg vis. ang., area of overlap 8 Â 8 deg). Each frame was filled with a transparent texture of blue and yellow or red and green stripes. The background had a mean luminance of 102 cd/m2, and the adapting stimuli had a mean luminance of 64 cd/m2 in the overlapping region. The color of the texture within each frame was randomly assigned for each trial. The orientation of the stripes was counterbalanced: half of the tri- als contained stripes perpendicular to the rectangles, half parallel to the rectangles. After the adapting period of each trial, all stimuli except the fix- ation point disappeared, and a tone sounded for 50 ms as a non-vi- sual attentional cue. Participants were instructed to pay attention to the vertical frame on trials when they heard a high tone, and Fig. 1. Example stimuli. Please refer to the web version of the article for color to the horizontal frame on trials when they heard a low tone. stimuli. Panel A corresponds to a ‘parallel stripes’ trial in Experiment 1. Panel B Immediately after the tone, the rectangular frames reappeared shows an example from Experiment 2. Panel C illustrates a trial from Experiment 3. for 10 s. Participants reported what they saw at each moment The reader can experience a demonstration of the effects by fixating in the center of one of the three colored stimuli for ten or more seconds, then shifting fixation to the within the square region of overlap between the two rectangles. empty frames at right, and attending to one of the two frames (or stripe They held one key if they saw vertical stripes, another if they orientations, in Panel C) The afterimage corresponding to the attended surface saw horizontal stripes, and a third if they saw a mixture of both should tend to be seen for longer periods than the unattended surface. orientations. They were instructed to hold the third key anytime the overlapping region was not exclusively filled by just one of inverse of the adapting stimulus, but the exact contents of the per- the two afterimage patterns (i.e., if there was any amount of piece- cept can be influenced by contextual cues presented during after- meal rivalry). Participants switched keys as often as necessary to image perception (Daw, 1962; van Lier, Vergeer, & Anstis, 2009). accurately reflect their visual experience, and released all the keys For post-retinal visual processes such as attention, afterimages when they no longer saw an afterimage. are likely equivalent to direct retinal input. The main advantage of using afterimages to study monocular rivalry is that afterimage 2.2. Results percepts are stabilized on the retina, and are therefore conve- niently immune to the confounding effects of eye movements that The average probability of every possible response at each mo- can otherwise influence monocular rivalry alternations (Crassini & ment of the response period can be seen in Fig. 2a. Responses con- Broerse, 1982; Georgeson, 1984). gruent with the attended stimulus are in green, those congruent In three experiments, we show that the mean dominance dura- with the unattended stimulus are in red, and mixed responses tion of attended afterimage surfaces engaged in monocular rivalry in