Abstract
Our perceptual system continually adapts to its sensory environment. As a result, both the neural representation of sensory information and perceptual behavior change with the adaptation state. However, it is unclear what fundamental principles guide these changes and how the perceptual and the neuronal changes relate to each other.
Here we extracted the adaptation induced changes in neural representation from psychophysical discrimination measurements using an information theoretic approach. We determined discrimination thresholds for visual orientation after prolonged adaptation to a broad-band grating stimulus with oblique (45 deg) orientation and compared them to thresholds measured for a non-orientated control adaptor that was matched in all other stimulus aspects (4 subjects). We found that after adaption to the oblique grating, the thresholds at the adaptor orientation and, surprisingly, perpendicular to the adaptor orientation were both substantially lower compared to the control condition. From these threshold measurements, we then estimated the adaptation induced changes in neural representation using an information theoretic bound (Cramer-Rao bound). Consistent with the threshold changes, encoding accuracy for orientations at and perpendicular to the adaptor orientation is higher than under the control condition, while it is lower in between.
The efficient coding hypothesis suggests that the extracted change in neural encoding accuracy ought to reflect the difference in stimulus statistics between the adaptation and control experiment. We found that the increase in encoding accuracy at the adaptor matches the relative increase in stimulus frequency during adaptation and thus is in agreement with the hypothesis. The increase at orientations perpendicular to the adaptor, however, is not explained. Our results provide an empirical basis for a systematic investigation into how adaptation changes the interpretation of sensory information (i.e. decoding), in particular, whether the perceptual system as a whole is “aware” of adaptation induced changes in sensory representations or not.