THE PERCEPTUAL-MAGNET EFFECT: AN EMERGENT CONSEQUENCE OF EXEMPLAR-BASED PHONETIC MEMORY

Abstract

This paper uses a mathematical model of infant speech perception to examine the assumptions and consequences of Kuhl's Native Language Magnet theory (NLM). A basic assumption of the NLM theory is that perceptual space is partitioned into phonetically relevant categories that are represented by category prototypes  the category's best exemplar. The category prototypes function as “perceptual magnets” that attract exemplars falling within their zone of influence. As a consequence, discrimination as a function of the auditory distance between a prototype and other exemplars is low in the neighborhood of the prototype and has an increasing positive derivative as the exemplar moves away from the prototype (discrimination is proportional to the square or the cube of the auditory distance between the prototype and the exemplar). While Kuhl's description of the perceptual magnet effect in terms of prototypes is elegant, I argue that the magnet effect emerges from a simple similarity metric operating on collections of exemplars stored in memory, without the need to refer to special exemplars.