P ERCEPTUAL BISTABILITY AS A TOOL FOR STUDYING UNCONSCIOUS VISUAL PROCESSING P IETER M OORS

Perceptual bistability Despite constant retinal input, perceptual experience changes continuously The processing of the suppressed stimulus can give insight into the neural correlates of visual awareness.

Paradigms Motion-induced blindness

Paradigms Motion-induced blindness Binocular rivalry and continuous flash suppression – See also the session on binocular rivalry

Paradigms Motion-induced blindness Binocular rivalry and continuous flash suppression – See also the session on binocular rivalry (Visual masking, inattentional blindness, change blindness, visual crowding, attentional blink, object substitution masking, …)

Measures Adaptation to the suppressed stimulus Priming by the suppressed stimulus Dominance/suppression durations Breaking suppression (CFS)

Overview Discuss findings on “low-level”, “mid- level”, and “high-level” aspects of suppressed stimuli End with discussion on the convergence and divergence between these findings

“Low-level” features The representation of very simple features seems to be preserved during suppression – Orientation (Blake & Fox, 1974; Blake et al., 2005; Montaser-Kouhsari et al., 2004; Moradi & Koch, 2005, …) – Spatial frequency (Yang & Blake, 2012, …) – Color (Hofstoetter et al., 2004, Hong & Blake, 2009) – Motion (Lehmkuhle & Fox, 1975; O’Shea & Crassini, 1981, …)

“Mid-level” features Gestalt grouping cues can influence dominance durations in – MIB (Bonneh et al., 2001; Mitroff & Scholl, 2005)

Bonneh et al. (2001)

Mitroff & Scholl (2005)

“Mid-level” features Gestalt grouping cues can influence dominance durations in – MIB (Bonneh et al., 2001; Mitroff & Scholl, 2005) – Binocular rivalry (Alais & Blake, 1999) Common fate Parallelism Good continuation

“Mid-level” features Mixed evidence for more complex Gestalts – E.g., Kanizsa stimulus Yes: Masking (Poscoliero et al., 2013); CFS (Wang et al., 2013) No: BR (Sobel & Blake, 2003), CFS (Harris et al., 2011)

Poscolieri et al. (2013)

Wang et al. (2012)

Sobel & Blake (2003)

Harris et al. (2011)

Moors et al. (in prep.) Divergence between direct and indirect measures in rivalry and CFS. Collinear contours of the pacmen could still drive the effect

Moors et al. (in prep.) Collinear contours of the pacmen could still drive the effect Extracting the surface is critical for the illusion Goal: Replicate effect from Wang et al. (2012) and use control stimuli for surface and collinear contours

Stimulus set Regular Irregular Kanizsa Regular Irregular KanizsaSurface Cross

b-CFS experiment Non dominant eyeDominant eye

Results N = 20 Main effect Stimulus and Regularity (BF = 48)

“High-level” features Faces – Adaptation in CFS Face shape only (Stein & Sterzer, 2011) Not identity (Moradi & Koch, 2005) Not gender or race (Amihai et al., 2011) – b-CFS findings Inversion effects (Jiang et al., 2007) Familiarity effects (Gobbini et al., 2013)

“High-level” features Emotional faces – Adaptation to emotional expressions (Adams et al., 2010) – Fearful faces break suppression faster (Yang et al., 2007) Potential spatial frequency confound? (Stein & Sterzer, 2011; Gray et al., 2013)

“High-level” features Semantic processing – In CFS Scene congruency biases suppression (Mudrik et al., 2010, 2011) For word stimuli – Prime – target congruency (Costello et al., 2009) – Emotional vs. neutral words (Yang & Yeh, 2011; Sklar et al., 2012)

“High-level” features Semantic processing – No study addressed whether words per se break suppression faster than pseudo/non- words – If words are processed, a word frequency effect is expected to be observed

Heyman and Moors (2014) Experiment 1 – Word type (word vs. pseudo-word) – Word frequency Experiment 2 – Pseudo words still readable Words vs. non-words – Letter familiarity Upright vs. inverted

Heyman and Moors (2014) N = 18 Null model (BF = 26)Null model (BF = 11)

Heyman and Moors (2014) N = 20 Null model (BF = 15)Null model (BF = 10)

Discussion Unconscious visual processing? – Findings often depend on the paradigm – Paradigms differ in their suppression mechanisms What does this imply for “unconscious” visual processing in general?

Discussion Are we learning something about unconscious visual processing? Or are we learning something about the level at which a suppression method acts and the representation of the stimulus at that level? Example: Kanizsa stimulus – CFS vs. masking vs. MIB

Discussion This point is increasingly being recognized – Breitmeyer (2014) “Much of brain imaging research relies on the use of one or another of the many noninvasive ways of rendering stimuli invisible. Without knowing at which cortical level of processing these blinding techniques exert their effects, one cannot make unequivocal claims as to what are or are not NCoCs and NCoUs.”

Discussion

– Fogelson et al. (2014) Continuous flash suppression versus Chromatic flicker fusion: