Adaptive heading performance during self‐motion perception

Abstract

Previous studies have documented that the perception of self-motion direction can be extracted from the patterns of image motion on the retina (also termed optic flow). Self-motion perception remains stable even when the optic-flow information is distorted by concurrent gaze shifts from body/eye rotations. This has been interpreted that extraretinal signals-efference copies of eye/body movements-are involved in compensating for retinal distortions. Here, we tested an alternative hypothesis to the extraretinal interpretation. We hypothesized that accurate self-motion perception can be achieved from a purely optic-flow-based visual strategy acquired through experience, independent of extraretinal mechanism. To test this, we asked human subjects to perform a self-motion direction discrimination task under normal optic flow (fixation condition) or distorted optic flow resulted from either realistic (pursuit condition) or simulated (simulated condition) eye movements. The task was performed either without (pre-and posttraining) or with (during training) the feedback about the correct answer. We first replicated the previous observation that before training, direction perception was greatly impaired in the simulated condition where the optic flow was distorted and extraretinal eye movement signals were absent. We further showed that after a few training sessions, the initial impairment in direction perception was gradually improved. These results reveal that behavioral training can enforce the exploitation of retinal cues to compensate for the distortion, without the contribution from the extraretinal signals. Our results suggest that self-motion perception is a flexible and adaptive process which might depend on neural plasticity in relevant cortical areas.

Heading perception depends on time-varying evolution of optic flow

“…This task, with the envelope motion stimuli, nearly replicated a previous study (10), and we refer the reader to their methods and figures for elaboration. The main differences between our study and theirs were: 1) We provided correct/incorrect feedback after each trial and they did not; 2) their translation rate was 2 m/s and ours was 1.5 m/s; 3) our stimuli consisted of circular plaid patches and theirs consisted of dots; and 4) our stimulus movie was 4 s in duration and theirs was 2.33 s. The average heading biases measured in that study were within 1°of ours, suggesting that, following training, biases are present with or without tone feedback (for time-varying stimuli), also consistent with the results of a perceptual learning study (49). Movement along a circular path avoids ambiguity about which coordinate system the heading judgment was made in (because retinocentric heading is constant over time) (10).…”

“…Other visual factors, such as stereo cues (38,39), depth structure (8,10,(40)(41)(42)(43), and field of view (FOV) (33,(42)(43)(44) can modulate the strength of these biases. Errors in heading judgments have been reported to be greater when eye (35-37, 45, 46) or head movements (37) are simulated versus when they are real, which has been taken to mean that observers require extraretinal information, although there is also evidence to the contrary (10,15,33,40,41,44,(47)(48)(49)(50). Regardless, to date no one has tested whether heading perception (even with these biases) is based on instantaneous optic flow or on the information available in how the optic flow field evolves over time.…”

Heading Perception Depends on Time-Varying Evolution of Optic Flow

“…Training ensured that observers understood the protocol and had reached asymptotic perceptual sensitivity in the task. One observer required only 120 trials of training in each condition (O5), but most required one or two hour-long training sessions (600 trials each) to achieve asymptotic performance on the task, consistent with previous reports (10,48). To determine when to end training and start the experiment, we checked that that discrimination accuracy was ~70-80% across all trials and ensured that the average converged heading values were consistent across the two interleaved staircases (for each rotation speed) and stable across runs of trials.…”

“…The main differences between our study and theirs were: 1) we provided correct/incorrect feedback after each trial and they did not; 2) their translation rate was 2 m/s and ours was 1.5 m/s; 3) our stimuli consisted of circular plaid patches and theirs consisted of dots; and 4) our stimulus movie was 4 seconds in duration and theirs was 2.33 seconds. The average heading biases measured in that study were within one degree of ours, suggesting that, following training, biases are present with or without tone feedback (for timevarying stimuli), also consistent with the results of a perceptual learning study (48). Movement along a circular path avoids ambiguity about which coordinate system the heading judgment was made in (because retinocentric heading is constant over time) (10).…”

“…Other visual factors such as stereo cues (37, 38), depth structure (8, 10,(39)(40)(41)(42), and field of view (32,(41)(42)(43) can modulate the strength of these biases. Errors in heading judgments have been reported to be greater when eye (34-36, 44, 45) or head movements (36) are simulated versus when they are real, which has been taken to mean that observers require extra-retinal information, although there is also evidence to the contrary (10,15,32,39,40,43,(46)(47)(48)(49). Regardless, to date, no one has tested whether heading perception (even with these biases) is based on instantaneous optic flow or on the information available in how the optic flow field evolves over time.…”