Uninformative visual experience establishes long term perceptual bias

Abstract

Visual appearance depends upon the resolution of ambiguities that arise when 2D retinal images are interpreted as 3D scenes. This resolution may be characterized as a form of Bayesian perceptual inference, whereby retinal sense data combine with prior belief to yield an interpretation. Under this framework, the prior reflects environmental statistics, so an efficient system should learn by changing its prior after exposure to new statistics. We conjectured that a prior would only be modified when sense data contain disambiguating information, such that it is clear what bias is appropriate. This conjecture was tested by using a perceptually bistable stimulus, a rotating wire-frame cube, as a sensitive indicator of changes in the prior for 3D rotation direction, and by carefully matching perceptual experience of ambiguous and unambiguous versions of the stimulus across three groups of observers. We show for the first time that changes in the prior-observed as a change in bias that resists reverse learning the next day-is affected more by ambiguous stimuli than by disambiguated stimuli. Thus, contrary to our conjecture, modification of the prior occurred preferentially when the observer actively resolved ambiguity rather than when the observer was exposed to environmental contingencies. We propose that resolving stimuli that are not easily interpreted by existing visual rules must be a valid method for establishing useful perceptual biases in the natural world.

Figure 1

Schematic representation of rotating cube task. a. The cube is disambiguated (informative). Front (filled) face of cube moves to the left, as does the dot; subject responds “front” (keypress ‘2’). b. The cube is disambiguated (informative). Back (unfilled) face moves left, as does the dot; subject responds “back” (keypress ‘8’). c. The cube is ambiguous (uninformative), but the subject clearly perceives one or other rotation and answers “front” or “back” accordingly. The direction of the probe dot was randomly allocated on each trial, so response was uncorrelated with apparent rotation. Arrows and shaded faces illustrate disambiguation in the figure; in the experiment rotation was disambiguated by binocular disparity and by occlusion (using an axial column similar to the one shown).

Figure 2

Schematic representation of experiment design. On Day 1, one group (“Informative”) viewed disambiguated cubes, with rotation direction contingent on location relative to a central fixation marker. A second group (“Uninformative”) viewed predominantly ambiguous cubes, but the percept of rotation was primed to be the same as that of the first group, by inclusion of some disambiguated cubes. On Day 2, all groups viewed a 50:50 mix of ambiguous and disambiguated cubes; disambiguated cubes had a rotation direction opposite to that which each subject had viewed on Day 1.

Figure 3

Difference in perceived rotation at the two cube locations on Day 1, assessed over all 480 trials in the session. Data points for 8 subjects in each of two groups. Horizontal lines are mean of group and error bars show s.e.m.

Figure 4

Difference in perceived rotation at the two cube locations on Day 2, assessed over the 240 ambiguous trials in the session. Perceptual outcome is assessed relative to the direction specified by disambiguated trials on Day 1. Data points for 8 subjects in each of two groups. Horizontal lines are mean of group and error bars show s.e.m.

Figure 5

Results from the 50:50 group; Day 1 perceptual experience over all 480 trials, Day 1 perceptual experience of 240 ambiguous trials only, Day 2 perceptual experience of 240 ambiguous trials only. Data points for 8 subjects. Horizontal lines are mean of group and error bars show s.e.m.