PSYC 2220 Lecture Notes - Lecture 3: Shining Light, Mach Bands, Lateral Inhibition

• School: York University
• Department: Psychology
• Course: PSYC 2220
• Professor: Ingo Frund

Document Summary

Special kind of eye structure: ommatidia: allow recordings from single receptors. Shining light into a single receptor leads to rapid firing of nerve fiber. Shining light into neighboring receptors leads to reduced firing rate of initial nerve fiber. Perceptual phenomena linked to lateral inhibition: the hermann grid: seeing spots at intersections, mach bands: seeding borders move sharply. Simultaneous contrast (chevreul illusion): seeing areas of different brightness due to adjacent areas. Lateral inhibition as explanation of the chevreul illusion: people see an illusion of enhanced lightness and darkness at borders of light and dark areas. Actual physical intensities indicate that this is not in the stimulus itself. Receptors responding to low intensity (dark) area have smallest output. Receptors responding to high intensity (light) area have largest output. The amount of inhibition is the same for all receptors. Assumption is the output of bipolar cells = excitation inhibition. On the low intensity side, there is additional inhibition resulting in enhanced darkness.