Journal of Vision (2016) 16(7):16, 1–11 1 Interaction between contours and eye movements in the perception of afterimages: A test of the signal ambiguity theory School of Psychology, Cardiff University, # Georgie Powell Cardiff, Wales, UK $ School of Psychology, Cardiff University, # Petroc Sumner Cardiff, Wales, UK $ School of Psychology, Cardiff University, James J. Harrison Cardiff, Wales, UK $ School of Psychology, Cardiff University, # Aline Bompas Cardiff, Wales, UK $ An intriguing property of afterimages is that conscious what is not perceived. A curious property of afterim- experience can be strong, weak, or absent following ages is that we do not perceive them as frequently—or identical stimulus adaptation. Previously we suggested for as long, as we ought to—based purely on the degree that postadaptation retinal signals are inherently of adaptation. Indeed, if our perception of afterimages ambiguous, and therefore the perception they evoke is correlated perfectly with the adaptation that produces strongly influenced by cues that increase or decrease the them, we would perceive them very often in the real likelihood that they represent real objects (the signal world, whereas in reality we perceive them rarely. ambiguity theory). Here we provide a more definitive Furthermore, they would not fluctuate in and out of test of this theory using two cues previously found to awareness as they often do (Comby, 1909; Wade, 1978). influence afterimage perception in opposite ways and plausibly at separate loci of action. However, by This perceptual instability is reminiscent of the manipulating both cues simultaneously, we found that alternating perceptual interpretations observed during their effects interacted, consistent with the idea that binocular rivalry or when viewing bistable figures. they affect the same process of object interpretation Further, the tendency of the visual system to prefer- rather than being independent influences. These findings entially allow meaningful information to reach aware- bring contextual influences on afterimages into more ness is evident in the quick fading of stabilized images general theories of cue combination, and we suggest that are artefacts of the retina (Coren & Porac, 1974) that afterimage perception should be considered and our propensity to discount the by-products of alongside other areas of vision science where cues are lighting conditions such as shadows (Rensink & found to interact in their influence on perception. Cavanagh, 2004). Afterimages have been studied for over two centuries by philosophers and scientists and they remain of interest to vision researchers today (e.g., Anstis, Geier, Introduction & Hudak, 2012; Aristotle, trans. 1910; Bessero & Plant, 2014; Darwin & Darwin, 1786; Hazenberg & van Lier, Our perception of afterimages seems to depend 2013; Sperandio, Chouinard, & Goodale, 2012; Sper- greatly on the conditions under which they are andio, Lak, & Goodale, 2012; van Lier, Vergeer, & experienced. This interesting feature renders them an Anstis, 2009; Wade, 2000). We now know that they are excellent tool to probe the general question of how probably generated from adaptation of cells in early early sensory signals are interpreted in the light of other visual pathways (Bachy & Zaidi, 2014; McLelland, available evidence to determine what is perceived and Ahmed, & Bair, 2009; Zaidi, Ennis, Cao, & Lee, 2012). Citation: Powell, G., Sumner, P., Harrison, J. J., & Bompas, A. (2016). Interaction between contours and eye movements in the perception of afterimages: A test of the signal ambiguity theory. Journal of Vision, 16(7):16, 1–11, doi:10.1167/16.7.16. doi: 10.1167/16.7.16 Received December 2, 2015; published May 18, 2016 ISSN 1534-7362 Downloaded from jov.arvojournals.org on 09/30/2021This work is licensed under a Creative Commons Attribution 4.0 International License. Journal of Vision (2016) 16(7):16, 1–11 Powell, Sumner, Harrison, & Bompas 2 Afterimages can either be of the same or complemen- could provide further evidence against an afterimage tary color/luminance to the adapting patch, depending representing a real object. on the intensity of the adapter stimulus and whether the During real life viewing, the visual scene is usually afterimage is viewed in the light or the dark. rich with contextual information and we make saccades Factors such as attention and eye movements during several times a second (Findlay & Walker, 1999), so eye adaptation can influence the resultant perception of movements and inconsistent contours will both be afterimages (Bachy & Zaidi, 2014; Lak, 2008; Suzuki & present most of the time; indeed, eye movements will Grabowecky, 2003; van Boxtel, Tsuchiya, & Koch, normally be what produce a change in local context 2010). However, our interest here is in the perception of (Coren & Porac, 1974). According to the signal afterimage percepts following the adaptation stage. ambiguity theory, this would explain why, even though Previous research found afterimage saturation to be adaptation occurs in everyday viewing, it leads only to increased by surrounding luminance edges (Daw, 1962; rare afterimage experiences. Our only occasional van Lier et al., 2009), and we have shown this increase perception of postadaptation signals despite available to be greater for afterimages than for real stimuli of evidence against them being a real object could be similar appearance (Powell, Bompas, & Sumner, 2012). attributed to the fact that calibration to the natural Thus, although the enhancement effect of edges on statistics of the world is not always complete (Bompas, afterimages and real-colored stimuli likely share some Powell, & Sumner, 2013). common mechanisms (Francis, 2010; Horwitz, Chi- However, there are other potential mechanisms that chilnisky, & Albright, 2005), the extra enhancement of might be sufficient to explain the effect of context and afterimages suggests that there is something inherently eye movements individually, without the need for the different about postadaptation signals. We also con- common process described in the ambiguity theory. firmed sporadic reports that saccadic eye movements The contextual influence could be a low-level effect of after the adaptation phase decrease the duration of shared receptive field properties for contours and color weak afterimages and reduce the probability of in V1 (see Powell et al., 2012 for discussion). On perceiving them at all (Ferree, 1908; Friedman & patterned backgrounds, the edge-related activity asso- Marchese, 1978; Helmholtz, 1962; Powell, Sumner, & ciated with eye movements (Ennis et al., 2014) may Bompas, 2015). shift the response range of neurons so that the One theory—hereafter referred to as the signal afterimages are more difficult to distinguish from the ambiguity theory—to explain the effect of these cues is background. On homogeneous backgrounds, where that postadaptation signals are inherently ambiguous contextual changes and local edge-related activity are because both the temporal properties of the signals and absent, eye movements may affect after images because their distribution across cortical areas are not like those perception can be biased towards the hue of the from real objects. In line with Bayesian perspectives, we postsaccadic location (usually the background gray) via would expect ambiguous signals to be particularly trans-saccadic integration mechanisms (Melcher, 2007; influenced by other information: cues that increase or also see Powell et al., 2015 for a full discussion). decrease the likelihood the signal represents a real Employing the classic approach of testing for object (Powell et al., 2012; Powell et al., 2015; also interactions, these separate accounts would predict recently echoed by Lupyan, 2015). Surrounding lumi- additivity between the two effects (Figure 1C). How- nance edges may increase the likelihood that the signal ever, an interaction between the two would suggest that is interpreted as a real object rather than as an the influence of contours and saccades partly occurs at irrelevant by-product of the visual system because the same level of visual processing and so would luminance edges often frame the boundaries of real support the signal-ambiguity theory (see Figure 1A, B). world objects (Fine, MacLeod, & Boynton, 2003; To date, the effects of context and eye movements have Hansen & Gegenfurtner, 2009; Sharman, McGraw, & been studied in isolation; studying how these two cues Peirce, 2013; Zhou & Mel, 2008). On the other hand, are combined provides both a more direct test of the saccadic eye movements may decrease this likelihood signal-ambiguity theory and also brings the study of because they cause the signal to move around in the afterimage perception in line with the wider cue world in a way that is unlike a real object. Indeed, combination literature. afterimages are stabilized on the retina and so their In the present experiments we aimed to test these two movement during saccades is perfectly correlated with hypotheses by measuring afterimage perception during the movement of the eyes, which is unlike the fixation and saccades and in the presence or absence of movement of any real world object (Coren & Porac, a luminance contour. Observers reported whether they 1974; Exner, 1890). Relatedly, afterimages will not had seen an afterimage at all, and if they had, they produce the strong edge-transients that typically occur reported its duration. Although previous studies have when the eyes move across a visual scene containing mainly relied