A confirmation bias in perceptual decision-making due to hierarchical approximate inference
Fig 4
Two task conditions that reduce either sensory or category information to threshold level using a staircase.
a) Each trial consisted of a 200ms start cue, followed by 10 stimulus frames presented for 83ms each, followed by a single mask frame of zero-coherence noise. After a 750ms delay, left or right targets appeared and participants pressed a button to categorize the stimulus as “left” or “right.” Stimulus contrast is amplified and spatial frequency reduced in this illustration. b) Category information is determined by the expected ratio of frames in which the orientation matches the correct category, and sensory information is determined by a parameter κ determining the degree of spatial orientation coherence (Methods). At the start of each block, we reset the staircase to the same point, with category information at 9: 1 and κ at 0.8. We then ran a 2-to-1 staircase either on κ or on category information. The Low-Sensory-High-Category (LSHC) and High-Category-Low-Sensory (HSLC) ovals indicate sub-threshold trials; only these trials were used in the regression to infer observers’ temporal weights. c) Visualization of a noisy stimulus in the LSHC condition. All frames are oriented to the left. d) Psychometric curves for all observers (thin lines) and averaged (thick line) over the κ staircase. Shaded gray area indicates the median threshold level across all observers. e) Example frames in the HSLC condition. The orientation of each frame is clear, but orientations change from frame to frame. f) Psychometric curves over frame ratios, plotted as in (d).