Nonvisual judgment of the crossability of path gaps.

The ability of persons to locomote without vision with the aid of a hand-held probe was investigated in 4 experiments focusing on the negotiation of gaps in a pathway. In Experiment 1, Ss of extreme heights judged under sighted and blindfolded conditions whether gaps of different sizes could be crossed by walking. Crossability boundaries were lower for shorter Ss, but the height effect disappeared under normalization by leg length. Experiments 2-4 altered mechanical aspects of the probe (length and mass distribution) in the nonvisual case. Ss' performance was still reliable in each experiment, and their performances were constrained by parameters of the gap and of their action systems. Probe variables, however, had surprisingly little influence on the judgments of crossability. Results were discussed in terms of potential roles for information in different perceptual modalities.     

Role of the inertia tensor in perceiving object orientation by dynamic touch.

Ss wielded an occluded L-shaped rod and attempted to perceive the direction in which the rod was pointing with respect to the hand. The pattern of the rod's different resistances to rotation in different directions, quantified by the inertia tensor, changes systematically with the rod's orientation. Perception of orientation by wielding is possible if the tissue deformation consequences of the rod's inertia tensor are detectable. It was shown that perceived orientation was a linear function of actual orientation for both free and restricted wielding and for rods of different-size branches. The eigenvectors of the inertia tensor were implicated as the basis for this haptic perceptual capability. Results were discussed in reference to information-perception specificity and its implications for effortful or dynamic touch.     

Asymmetric dependencies in perceiving identity and emotion: Experiments with morphed faces

We investigated whether an asymmetric relationship between the perception of identity and emo-tional expressions in faces (Schweinberger & Soukup, 1998) may be related to differences in the rela-tive processing speed of identity and expression information. Stimulus faces were morphed across identity within a given emotional expression, or were morphed across emotion within a given identity. In Experiment 1, consistent classifications of these images were demonstrated across a wide range of morphing, with only a relatively narrow category boundary. At the same time, classification reaction times (RTs) reflected the increased perceptual difficulty of the morphed images. In Experiment 2, we investigated the effects of variations in the irrelevant dimension on judgments of faces with respect to a relevant dimension, using a Garner-type speeded classification task. RTs for expression classifica-tions were strongly influenced by irrelevant identity information. In contrast, RTs for identity classifi-cations were unaffected by irrelevant expression information, and this held even for stimuli in which identity was more difficult and slower to discriminate than expression. This suggests that differences in processing speed cannot account for the asymmetric relationship between identity and emotion per-ception. Theoretical accounts proposing independence of identity and emotion perception are dis-cussed in the light of these findings.     

Understanding covert recognition

An implementation of Bruce and Young's (1986) functional model of face recognition is used to examine patterns of covert face recognition previously reported in a prosopagnosic patient, PH. Although PH is unable to recognize overly the faces of people known to him, he shows normal patterns of face processing when tested indirectly. A simple manipulation of one set of connections in the implemented model induces behaviour consistent with patterns of results from PH obtained in semantic priming and interference tasks. We compare this account with previous explanations of covert recognition and demonstrate that the implemented model provides the most natural and parsimonious account available. Two further patients are discussed who show deficits in person perception. The first (MS) is prosopagnosic but shows no covert recognition. The second (ME) is not prosopagnosic, but cannot access semantic information relating to familiar people. The model provides an account of recognition impairments which is sufficiently general also to be useful in describing these patients.     

Categories and boundaries in speech and music*

Perceptual categories and boundaries arise when Ss respond to continuous variation on a physical dimension in a discontinuous fashion. It is more difficult to discriminate between members of the same category than to discriminate between members of different categories, even though the amount of physical difference between both pairs is the same. Speech stimuli have been the sole class of auditory signals to yield such perception; for example, each different consonant phoneme serves as a category label. Experiment I demonstrates that categories and boundaries occur for both speechand nonspeech stimuli differing in rise time. Experiment II shows that rise time cues categorical differences in both complex and simple nonspeech waveforms. Taken together, these results suggest that certain aspects of speech perception are intimately related to processes and mechanisms exploited in other domains. The many categories in speech may be based on categories that occur elsewhere in auditory perception.     

Book review

Reber, A. S. and Scarborough, D. L. Toward a Psychology of Reading. Hillsdale, N. J.: Lawrence Erlbaum Associates. 1977. Pp. xii + 337. £13.50. ISBN 0470 99010 4.

Medin, D. L., Roberts, W. A. and Davis, R. T. Process of Animal Memory. Hillsdale, New Jersey: Lawrence Erlbaum Associates. 1976. Pp. 267. £ 11.50. ISBN 0 470 15189 7.

Myers, R. D. (Ed.). Methods in Psychobiology, Vol. III. New york: Academic Press. 1977. Pp. 339. £14.20. ISBN 0 12 4610 03 X.

Estes, W. K. (Ed.). Handbook of Learning and Cognitive Processes, Volume 2. Conditioning and Behavior Theory. Hillsdale, New Jersey: Lawrence Erlbaum Associates. 1975. Pp. 373. ISBN 0 470 24586 7.     

Evaluation of a healthy-weight treatment program for bulimia nervosa: a preliminary randomized trial

Objective: Conduct a randomized treatment trial to test whether healthy dieting maintains bulimic symptoms or effectively reduces this eating disturbance.

Methods: Female participants (n=85) with full- and sub-threshold bulimia nervosa were randomly assigned to a 6-session healthy dieting intervention or waitlist condition and assessed through 3-month follow-up.

Results: Relative to control participants, intervention participants showed modest weight loss during treatment and demonstrated significant improvements in bulimic symptoms that persisted through follow-up.

Discussion: These preliminary results suggest that this intervention shows potential for the treatment of bulimia nervosa and may be worthy of future refinement and evaluation. Results also provide experimental evidence that dieting behaviors do not maintain bulimia nervosa, suggesting the need to reconsider maintenance models for this eating disorder.     

The differential effects of intrinsic and identified motivation on well-being and performance: prospective, experimental, and implicit approaches to self-determination theory

Self-determination theory research has demonstrated that intrinsic and identified self-regulations are associated with successful adaptation. However, few distinctions are typically made between these regulations and their outcomes. In the present studies, the associations between intrinsic and identified motivations and outcomes of psychological well-being and academic performance are compared in educational settings. In Study 1, intrinsic self-regulation predicted psychological well-being, independent of academic performance. In contrast, identified regulation predicted academic performance. Additionally, the more that students demonstrated an identified academic regulation, the more that their psychological well-being was contingent on performance. In Study 2a, priming intrinsic self-regulation led to greater psychological well-being 10 days later. In Study 2b, an implicit measure of identified regulation predicted academic performance 6 weeks later. Results indicate the need to address important distinctions between intrinsic and identified regulations.