Separating perceptual processes from decisional processes in identification and categorization

Generalizing a neuropsychological model of visual categorization to auditory categorization of vowels

“…Our intuition is that this assumption is generally incorrect and that the necessity to relax it depends most on the procedural aspects of the experiment. For example, with highly confusable stimuli, short exposure durations, or masked displays, the influence of perceptual noise on performance is increased, and the stimulus invariance assumption will more likely need to be relaxed (e.g., Maddox, 2001Maddox, , 2002. In the present study, though, the stimuli are highly discriminable, are not masked, and are of reasonable exposure durations.…”

“…The response regions depicted in Figure 1b are not optimized in any sense; that is, they are not constructed in such a way as to maximize long-term accuracy. However, evidence with visually presented stimuli suggests that with experience, observer's response regions, as modeled with the SPC, do become more nearly optimal (Maddox, 2001(Maddox, , 2002. Hypothetical minimum-distance response regions for the same stimuli but where two striatal units are associated with each category are displayed in Figure 1c.…”

“…In identification,on the other hand, each vowel stimulus would have its own unique response label. SPC models of identification Maddox, 2001Maddox, , 2002 could then be used to provide an estimate of the underlying perceptual representations for each vowel stimulus. These could then be held fixed in an attempt to model the vowel categorization performance.…”

Indecision on decisional separability

“…The key focus of our critique was a form of dimensional interaction called mean shift integrality (e.g., see Maddox, 2001), a violation of perceptual separability in the language of GRT. It has been long acknowledged that the standard application of MSDA, including the widely used MSDA_2 2 We also conducted simulated violations of PS caused by differences in variance along particular values of dimensions, keeping means constant.…”

“…Applying GRT to empirical data to uncover perceptual and decisional loci of dimensional interactions has been performed using two main approaches. One approach involves fitting models to observed data that impose parameter constraints that implement particular violations of GRT constructs (e.g., Ashby & Lee, 1991;Macho, 2007;Maddox, 2001;Maddox & Bogdanov, 2000;Thomas, 2001;Wickens, 1992). Analysis and comparison of these models permits inferences about which GRT constructs hold and which are violated for a given task and stimulus set.…”