Can attention selectively bias bistable perception? Differences between binocular rivalry and ambiguous figures

Abstract

It is debated whether different forms of bistable perception result from common or separate neural mechanisms. Binocular rivalry involves perceptual alternations between competing monocular images, whereas ambiguous figures such as the Necker cube lead to alternations between two possible pictorial interpretations. Previous studies have shown that observers can voluntarily control the alternation rate of both rivalry and Necker cube reversal, perhaps suggesting that bistable perception results from a common mechanism of top-down selection. However, according to the biased competition model of selective attention, attention should be able to enhance the attended percept and suppress the unattended percept. Here, we investigated selective attentional modulation of dominance durations in bistable perception. Observers consistently showed much weaker selective attentional control for rivalry than for Necker cube reversal, even for rivalry displays that maximized the opportunities for feature-, object-, or space-based attentional selection. In contrast, nonselective control of alternation rate was comparably strong for both forms of bistable perception and corresponded poorly with estimates of selective attentional control. Our results support the notion that binocular rivalry involves a more automatic, stimulus-driven form of visual competition than Necker cube reversal, and as a consequence, is less easily biased by selective attention.

Figure 1

A. Necker cube stimuli in Experiment 1. Only one of the three crosshairs was presented in each trial as a fixation point. B. Binocular rivalry stimuli in Experiment 2. The contrast of the face was kept fixed at 30% while the contrast of the house was manipulated on each trial (15, 30, or 60%). C. Binocular rivalry stimuli in Experiment 4. The contrast of the left-tilted grating decreased linearly from left to right and the right-tilted grating increased from left to right (contrast range 10–90%).

Figure 2

Mean normalized dominance durations for perceiving the bottom view (left) and top view (right) during selective attentional control of the Necker cube in Experiment 1 (N = 16). Observers were instructed either to passively view the Necker cube (black solid line), to try to attend to the bottom view interpretation (green dashed line), or to try to attend to the top view interpretation (red dotted line). Error bars represent ±1 SEM. Note that selective attention both facilitated the perception of the attended percept and inhibited perception of the unwanted percept, consistently across all fixation positions.

Figure 3

Mean normalized dominance durations for perceiving face (left) and house (right) during selective attentional control of binocular rivalry in Experiment 2 (N = 16). Observers were instructed to attend to the face (green dashed line), attend to the house (red dotted line), or passively view the stimuli (black solid line). The contrast of the house was manipulated while the contrast of the face was set to 30%. Error bars represent ±1 SEM. Selective attention led to weak modulations in dominance duration, as compared to bottom-up manipulations of stimulus contrast.

Figure 4

Mean normalized dominance durations for perceiving the bottom view (left) and top view (right) during selective attentional control of the Necker cube in Experiment 3 (N = 6). Observers were instructed to attend to the bottom view (green dashed line), attend to the top view (red dotted line), or passively view the Necker cube (black solid line). Error bars represent ±1 SEM.

Figure 5

Mean normalized dominance durations for perceiving face (left) and house (right) during selective attentional control of rivalry in Experiment 3 (N = 6). Observers were instructed to attend to the face (green dashed line), attend to the house (red dotted line), or passively view the stimuli (black solid line). The contrast of the house was manipulated while the contrast of the face was set to 30%. Error bars represent ±1 SEM.

Figure 6

Comparison of the proportion of selective attentional modulation for Necker cube reversal and binocular rivalry (Experiments 1–3). Bar graphs indicate the proportion of modulation in mean dominance duration for each attentional condition relative to passive viewing. A. Data of naïve observers in Experiments 1 and 2. B. Data of experienced observers in Experiment 3. Asterisks indicate statistically significant modulations relative to passive viewing (*p < .05; **p < .01; ***p < .001). Error bars represent ±1 SEM. For Necker cube reversal, selective attention significantly increased the attended percept and decreased the unattended percept, whereas attentional modulation of binocular rivalry was weak and unreliable.

Figure 7

A. Comparison of the proportion of voluntary control over alternation rates for Necker cube reversal and binocular rivalry in Experiment 3. Bar graphs indicate the proportion of modulation in alternation rate for each voluntary control condition relative to passive viewing. Error bars represent ±1 SEM. Observers showed a strong ability to modulate the alternation rates of both Necker cube reversal and binocular rivalry. B. Normalized rates of alternation across contrast levels for binocular rivalry. Observers showed substantial control of rivalry alternation rates, and could roughly double the rate of fast alternations as compared to slow alternations. Moreover, the amount of control over rivalry alternations significantly increased as a function of stimulus contrast.

Figure 8

Mean normalized dominance durations for perceiving the left-tilted grating and right-tilted grating during selective attentional control of a spatially biased rivalry display in Experiment 4 (N = 6). Rivalry stimuli varied in contrast from left to right, to induce a physical spatial bias (see Figure 1c). Observers were instructed either to passively view the display (black solid line), to attend to the left side corresponding to the high-contrast portion of the left-tilted grating (green dashed line), or to attend to the right side corresponding to the high-contrast portion of the right-tilted grating (red dotted line). Error bars represent ±1 SEM. Shifts in fixation position strongly biased percept durations, whereas shifts in spatial attention led to poor selective control of rivalry.

Figure 9

Proportion of modulation for the bottom-up effect of fixation position (left) and the top-down effect of spatial attention (right) in biasing binocular rivalry in Experiment 4. Error bars represent ±1 SEM. Note that shifts of fixation position led to overall modulations of about 30%, whereas shifts of spatial attention led to much weaker modulations of only about 10%.