Abstract
Modulation of perceptual discrimination of simple physical dimensions characterize three related phenomena: categorical perception (e.g., Roberson et al. 2000; JEP General, 369–398); the perceptual magnet effect (e.g. Guenther et al., 1999; JOSA, 2900–2912); and prototype-bias (Huttenlocher et al., 2000; JEP General, 220–241). In categorical perception cross-category discrimination easier than equivalent within-category discrimination; with the perceptual magnet, discrimination close to the prototype is harder than far from the prototype; and in prototype-bias, memory errors are biased towards the prototype increasing as the trace attenuates. Here we investigate the relations among the three phenomena in hue perception, and consider their relationship to stimulus labeling.
The stimuli varied in Munsell hue (constant value and chroma) and discrimination was measured using a successive same-different task with a 5-sec. ISI; different-pairs were separated by the same number of hue units, within an experiment. Experiment 1 required judgements around the prototype of the blue and green categories and established that the perceptual magnet and prototype-bias occurred for color, and that their effect was additive. Subjects then learned new categories by splitting blue or green into two, and categorical perception was found around the new boundary. However, categorical perception appeared to be independent of prototype-bias. Experiment 2 used stimuli from the blue-green boundary and included either verbal or visual interference in the ISI. With no interference, both categorical perception and prototype-bias were found, but categorical perception was eliminated by verbal interference.
We conclude that categorical perception and prototype-bias are independent phenomena, but categorical perception may be due to the same process as perceptual magnet and both may be related to naming.