Academic journal article Memory & Cognition

Identity Categories and Transformational Paths for Face Changes across the Age Spectrum

Academic journal article Memory & Cognition

Identity Categories and Transformational Paths for Face Changes across the Age Spectrum

Article excerpt

Published online: 11 September 2013

# Psychonomic Society, Inc. 2013

Abstract How faces change across lengthy time periods and whether the changing appearance of a face functions as an identity category was investigated in two experiments. In Experiment 1, the faces of 15 individuals were multidimensionally scaled at each of seven age epochs (roughly <6 months to 75 years of age) and correlated with the same persons, but at different ages. In Experiment 2, three individuals at each of seven age epochs were multidimensionally scaled, and analyses explored the conceptual structure and transformational path of each person within the space. The results revealed that even the earliest age epochs (<6 months) were correlated with the later epochs, except for the most extreme age, with the correlation highest at intermediate ages. Transformational paths were found that emerged and terminated at haphazard points in the space. Results are discussed in terms of principled change in categories whose members systematically change across their life cycle, including suggestions for the need to incorporate systematic change in current theories of categorization.

Keywords Categorization . Concepts . Face processing . Memory . Schema

A remarkable facet of our world is that it is in a constant state of flux. Objects enter our consciousness, while others depart. Over longer time periods, even the same object changes, what Bruner, Goodnow, and Austin (1956)referredtoasanidentity category. Remarkably, humans adjust to the endless changes in the environment with surprisingly little difficulty. We expect friends not seen in ages to look different (although we say otherwise!), but in predictable ways. Anecdotally, children learn about changes early in life-that caterpillars become butterflies and tadpoles become frogs, that a planted seed gives rise to a seedling, that gardens grow, and that blossoms become fruit. Certain forms of expertise entail sophisticated knowledge of how change is manifested, such as in early detection of cellular development of normal and cancerous cells (Muller, Rambaek, Hovig, & Hovig, 1991). The concept of change even finds its way into our art and poetry:

. . . but one man loved the pilgrim soul in you, And loved the sorrows of your changing face.1

Nonetheless, how things change and how this knowledge is incorporated into our concepts has received little attention. The vast majority of experiments in human categorization adheres to a design whereby the subject learns (typically) two categories, each composed of a handful of instances that need have little in common other than a common name (e.g., Homa, 1984). An instance may be encoded differently across trials, but physically, the instance remains a static entity throughout the learning procedure. As such, these approaches fail to address the issues of concern here-how members evolve and what mechanism binds them together, other than their name.

The present study used photographs of actual human faces that spanned a wide range in age, roughly from 4 to 6 months to 70 years of age. Our overriding interest was whether the changing face across an extended range in time would cohere as a structured category in multidimensional space and would produce a discernible path (Experiments 1 and 2). The use of multidimensional scaling (Kruskal, 1964;Shepard,1962)was selected as a measure of uncovering structure, since the resulting spaces containing the various persons generated by similarity ratings can be readily inspected to investigate the major issues of interest: (1) Are similarities and dissimilarities among the scaled persons roughly maintained from the earliest to later ages (Experiment 1), and (2) does each person trace out a discernible path within a multidimensional space as they age (Experiment 2)? Both experiments provide insight into how an identity category might be revealed. Experiment 1 recalls the proverb, "The more things change, the more they stay the same. …

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