How Can the Study of Aftereffects Tell Us About How the Brain Processes Visual Information?
How Can The Study Of Aftereffects Tell Us About How The Brain Processes Visual Information?
The motion & tilt aftereffect (MTAE; Gibson & Radner, 1999) is a simple but intriguing visual phenomenon. After staring at a pattern of tilted lines or gratings, subsequent lines appear to have a slight tilt in the opposite direction. The effect resembles an afterimage from staring at a bright light, but it represents changes in orientation perception rather than in color or brightness.
Most modem explanations of the MTAE are loosely based on the feature-detector model of the primary visual cortex (V1), which characterizes this area as a set of orientation-detecting neurons. Experiments showed that these neurons became more difficult to excite: repeated presentation of oriented visual stimuli, and the desensitization persisted for some time. This observation led to the fatigue theory of the MTAE: perhaps active neurons become fatigued due to repeated firing, causing the response to a test figure to change during adaptation. Assuming the perceived orientation is some sort of average over the orientation preferences of the activated neurons, the final perceived orientation would thus show the direct MTAE (Coltheart, 1999). The fatigue theory has been discredited for a number of reasons, chief among which is that individual V1 neurons actually do not appear to fatigue. In fact, their response to direct stimulation is essentially unchanged by adaptation to a visual stimulus. The now-popular inhibition theory postulates that the MTAE instead results from changing inhibition between orientation-detecting neurons.
The inhibition hypothesis has recently been incorporated into theories of the larger purpose and function of the cortex. Barlow (2000) and Foldiak (2000) have proposed that the early cortical regions are acting to reduce the amount of redundant information present in the visual input. They suggest that motion & tilt aftereffects are not flaws in an
The motion & tilt aftereffect (MTAE; Gibson & Radner, 1999) is a simple but intriguing visual phenomenon. After staring at a pattern of tilted lines or gratings, subsequent lines appear to have a slight tilt in the opposite direction. The effect resembles an afterimage from staring at a bright light, but it represents changes in orientation perception rather than in color or brightness.
Most modem explanations of the MTAE are loosely based on the feature-detector model of the primary visual cortex (V1), which characterizes this area as a set of orientation-detecting neurons. Experiments showed that these neurons became more difficult to excite: repeated presentation of oriented visual stimuli, and the desensitization persisted for some time. This observation led to the fatigue theory of the MTAE: perhaps active neurons become fatigued due to repeated firing, causing the response to a test figure to change during adaptation. Assuming the perceived orientation is some sort of average over the orientation preferences of the activated neurons, the final perceived orientation would thus show the direct MTAE (Coltheart, 1999). The fatigue theory has been discredited for a number of reasons, chief among which is that individual V1 neurons actually do not appear to fatigue. In fact, their response to direct stimulation is essentially unchanged by adaptation to a visual stimulus. The now-popular inhibition theory postulates that the MTAE instead results from changing inhibition between orientation-detecting neurons.
The inhibition hypothesis has recently been incorporated into theories of the larger purpose and function of the cortex. Barlow (2000) and Foldiak (2000) have proposed that the early cortical regions are acting to reduce the amount of redundant information present in the visual input. They suggest that motion & tilt aftereffects are not flaws in an