|
Psychophysical calibration of internal standards| old_uid | 2583 |
|---|
| title | Psychophysical calibration of internal standards |
|---|
| start_date | 2007/04/02 |
|---|
| schedule | 11h-12h30 |
|---|
| online | no |
|---|
| summary | After we have adapted to a red patch, a yellow patch in the same part of the visual field will look green. After we have adapted to downwards motion (for example, a waterfall) stationary contours will appear to move upwards. Adaptation to a male face makes an androgynous face look more female. Are these changes caused by loss of sensitivity in an adapted mechanism, or to a recalibration of an internal standard ? The most widely-held model of the motion aftereffect (the MAE for short) asserts that it is due to a change in relative gain of the two inputs to an opponent mechanism. However, existing evidence does not clearly distinguish between this mechanism and an additive signal to the opponent stage (recalibration). Some data favour recalibration, for example, the finding that the MAE is reduced when the adapting motion is correlated with self-motion. The finding that lack of attention to the adapting stimulus reduces the MAE is also consistent with recalibration. It might be thought that sensitivity change and recalibration make very different predictions for the shape of the psychometric function in a motion classification task, but we shall present the results of modelling showing that this is not the case. To see whether changes in gain control are sufficient to explain the MAE we measured the effect of adaptation on the contrast discrimination function (the T vs C ‘dipper’ function) for gratings moving in the adapted and non-adapted directions. We used the transducer functions derived from these functions to try to predict the change in the null point for a mixture of oppositely moving gratings of different contrast. In general the prediction was accurate, but with a small discrepancy in the direction predicted by a recalibration. We suggest this as a general strategy for deriving Type 2 measures (bias) from Type 1 (sensitivity) changes. Data on the effects of attention on bias and sensitivity will be described. |
|---|
| responsibles | Information non disponible |
|---|
| |
|