Competition between newly recruited and pre-existing visual cues during the construction of visual appearance

Abstract

During perception, conflicting visual cues often trade against each other. Recent cue recruitment experiments show that the visual system can be conditioned to use artificial visual cues during the perception of a bistable stimulus. Does the visual system treat the new cue as an independent source of information, separate from the long-trusted cues that were used to train it? If so, presence of the long-trusted cue should not be sufficient to block the new cue's effect. Here, we show that a newly recruited cue (stimulus location) and a long-trusted, pre-existing cue (binocular disparity) trade against each other: they contribute simultaneously to the direction of perceived 3D rotation of a Necker cube. We also show that the new position cue was based primarily on retinal position, so early visual areas may mediate the cue's effect.

Fig. 1

Task (a) and stimulus (b). A dot was displayed near the fixation mark (a). On each trial it moved either left or right with equal probability, and the trainee pressed “2” if the dot appeared to move with the front of the cube, or “8” if it moved with the back. For the figure shown, the correct answer would be “8”. The left and middle pictures in (b) show training stimuli, containing both the long-trusted depth cues (stereo and occlusion) and the new cue (stimulus position). In the configuration shown, the cube rotates leftward when it is below the fixation mark and rightward when it is above. By arbitrary definition, position and rotation direction are “positively” correlated in these panels; negative correlation for these cues is simply the opposite (rightward below fixation mark, leftwards above). The rightmost panel shows a test trial; it contains the position cue and a weak disparity cue that favors rightward rotation. Yellow arrows indicate object rotation direction.

Fig. 2

Results from Experiment 1: Tradeoff between newly recruited cue and long-trusted cue. POSN was correlated with long-trusted cues on training trials for eight trainees in the test condition (left graphs), and uncorrelated for eight trainees in the control condition (right graphs). The abscissa is the disparity added to the rotating cube on test trials. The ordinate is the percentage of test trials seen as having right-hand rotation. Each data point was computed from 30 test trials. Curves are maximum likelihood fits for a pair of cumulative Gaussians sharing a common slope (so there were three free parameters in the fit: μ₁, μ₂, and σ). In the test condition, half of the trainees (upper 4 panels on the left) viewed training trials with positive correlation and half (lower 4 panels on the left) viewed training trials with negative correlation; hence the TOP and BOTTOM data are shifted in different directions in the upper 4 panels as compared to the lower 4 panels. This separation is not observed for the control group.

Fig. 3

Results from Experiments 2 and 3, showing that the new POSN cue had a long lasting effect. Top panels show data from a single trainee in each experiment, respectively, in the format of Figure 2, for Days 1 and 2 (Experiment 2, left) or for the first and second half of the session (Experiment 3, right). The bottom panels plot vertical separation between the two fitted psychometric functions for all trainees in each experiment, respectively. Initial training in each experiment was counterbalanced across trainees (half positive correlation, solid lines; half negative, dashed lines). In Experiment 2, all trainees showed additional reliance on POSN in the second session as compared to the first (p < .01 for 3 of the 4 trainees, normal test using estimated standard errors). In Experiment 3 the correlation between POSN and long-trusted cues was reversed half way through the experiment. The first 20% of each half session is excluded from the analysis. All trainees unlearned the initial correlation to some extent during the second half of the session, and some trainees achieved reversal, but no trainee learned the reversed correlation as strongly as the initial correlation. Thus, learning from the first half lasted longer than just a few trials. Error bars are the standard deviation of 2000 bootstrap estimates (Efron & Tibshirani, 1993) of the vertical separation of the two curves, fitted using the same procedure as with the original data in Experiment 1. Small horizontal offsets in bottom panels are to make the data easier to see.

Fig. 4

Experiment 4 display configuration, that made rotation direction (as specified by long-trusted cues) contingent on either retinal or world position during training. Both fixation marks were visible at all times and the trainee was instructed which mark to fixate on each trial by a flashing circle (shown for right fixation mark). The rotating cube always appeared to the left or right of fixation (at one of the locations shown by the dashed marks). To train retinal position, the cube on training trials had rightward rotation if it appeared to the right of fixation, and leftward rotation if to the left of fixation (or vice versa, counterbalanced across trainees). To train world position, the cube on training trials had rightward rotation at the center location and leftward rotation at the two side locations (or vice versa). Different groups received retinal and world training, respectively.