Face perception is often characterized as depending on configural, rather than part-based, processing. Here we examined the relative contributions of configuration and parts to early "face-selective" processing at the M170, a magnetoencephalographic response approximately 170 ms after stimulus onset, using adaptation. Previously (Harris and Nakayama 2007), we showed that rapid successive presentation of 2 stimuli (stimulus-onset asynchrony < 800 ms) attenuates the M170 response. Such adaptation is face-selective, with greater attenuation when faces are preceded by other faces than by houses. This technique therefore provides an independent method to assess the nature of this early neurophysiological marker. In these experiments, we measured the adapting power of face configurations versus parts using upright and inverted faces (Experiment 1), face-like configurations of black ovals versus scrambled nonface configurations of face parts (Experiment 2), and isolated face parts (Experiment 3). Although face configurations alone do not produce face-selective adaptation, scrambled and even isolated face parts adapt the M170 response to a similar extent as full faces. Thus, at least for the relatively early face-selective M170 response, face parts produce face-selective adaptation but face configurations do not. These results suggest that face parts are important at relatively early stages of face perception.
It is well known that human beings are poor random generators (Wagenaar, 1972). For example, people have difficulty in creating random number sequences. What underlies this behavioral tendency? In order to examine this, we investigate the kinds of environments that can alter this ability to generate randomness. Subjects selected and mouse-clicked three different buttons in the designated field on the computer display (there are 4X4 square buttons). In each trial, subjects were asked to make the three button combination that they have never created before, that is, “a new combination”. One subject group did the task while listening to the radio, another group without listening to the radio. The degree of randomness was assessed quantitatively. We find that the averaged level of randomness of the subjects group listening to the radio is significantly higher than the group without the radio. Although the achievement of the group with radio was still worse than the pseudo-random combinations generated by a computer, the auditory distractor led to more random combinations. The present results are in accord with previous findings that show that people are poor random generators. At the same time, it suggests that reducing a subject's concentration on the task enhances the ability to generate randomness or attenuates suppression of more stereotyped behavior. However, to understand the mechanisms underlying this phenomenon, further psychophysical and physiological experiments are required.
