On the Distinctive Features of Ecological Laws

Ecological psychology is grounded in the assumption of the availability of lawlike regularities in the world as the basis of reliable information for perceiving-acting systems. This article aims to articulate some of the necessary conditions for an account of lawfulness that accommodates ecological theories of perceiving and acting. This attempt considers historically influential accounts of laws but offers modifications of the notions of law and especially of cause that are of greater relevance to the practice of an ecological science. A guiding assumption is that the laws of the animate are the most general. The authors advocate understanding laws in reference to reliable regularities, causes as not being strictly Newtonian in character, and flexibility with respect to certain formal and philosophical commitments.     

Dynamics of 1:2 Coordination: Temporal Scaling,Latent 1:1, and Bistability

The simplest interlimb multifrequency coordination of 1:2 can be performed at different speeds and in at least two different styles or modes. The effects of speed and mode (in-phase or antiphase) were evaluated in a bimanual 1:2 rhythmic task in which participants (N = 8) oscillated hand-held pendulums with identical or different uncoupled frequencies. A motion equation in relative phase that captures the asymmetries of components and task predicted the 1:2 coordination equilibria resulting from temporal scaling. According to the experimental results, both coordination modes proved to be equally stable. More detailed analyses of individual trials showed signs that the more fundamental 1:1 coordination intruded into the 1:2 coordination.     

A Note on the Natural Basis of Action Categories

What is the basis for the categorical distinctions evident in action? For some visually-guided activities it can be shown that categories of action are specified by criterial values of optical properties. In the more general case, the criterial optical properties should be scaled relative to dimensions of the acting animal. The analysis of the prey-catching behavior of praying mantids is used to exemplify the strategy for determining naturally defined boundaries on actions.     

Principles of part-whole selective perception by dynamic touch extend to the torso

The haptic subsystem of dynamic touch expresses a novel form of part-whole selective perception. When wielding a nonvisible rod grasped at some intermediate point along its length, an individual can attend to and report the length of a part of the rod (e.g., the segment forward of the hand) or the length of the whole rod. Both perceptions relate to the rod's mass moments about the point of grasp but in systematically different ways. Previous demonstrations of this part-whole selectivity have been in respect to rods grasped by hand or attached to a foot. The authors demonstrated the part-whole selectivity for nonvisible rods attached to the shoulder girdle and wielded primarily by movements of the trunk with benchmark performance provided by the same rods grasped and wielded by hand. Their results suggest that part-whole selectivity is a haptic capability general to the body.     

Phonological codes are early sources of constraint in visual semantic categorization

Two experiments were directed at early phonological activation in the semantic categorization task. In Experiment 1, briefly exposed targets homophonic to category exemplars (rows for the categorya flower), and their graphemic controls (robs), were judged for category membership with and without a backward pattern mask False positives were greater for rows than robs to the same degree under both unmasked and masked conditions. In Experiment 2, false positives were examined in the semantic categorization task under backward dichoptic masking by pseudowords that were, in turn, masked monoptically by a pattern mask. Briefly exposed homophones (e.g.,weak), masked by a phonologically similar pseudoword (“feek”), a graphemic control (“felk”), or an unrelated pseudoword (“furt”), were categorized as category exemplars (a unit of time). The difference in false positives was significant forweak-feek versusweak-furt, but not forweak-felk versusweak-furt. It was suggested that the persistence of the homophonic effects under the pattern masking of Experiment 1 and their amplification under the phonological masking of Experiment 2 were because phonological codes cohere rapidly and provide, thereby, immediately available constraints on semantic processing.     

Chaos in Human Rhythmic Movement

Rhythmic movements typical of locomotory actions are usually modeled as limit cycle dynamics, and their deviations from pure periodicity are attributed to stochastic physiological noise. In the present study, the dynamics of human rhythmic movements were found to contain more than the 2 dynamically active variables expected from limit cycle dynamics; the number depended upon the size of the limb oscillator. Observed positive Lyapunov exponents and fractal attractor dimensions indicated that the gross variability of human rhythmic movements may stem largely from low-dimensional chaotic motion on strange attractors.     

Dynamical aspects of learning an interlimb rhythmic movement pattern

Learning a bimanual rhythmic task is explored from the perspective that motor skill acquisition involves the successive reparameterization of a dynamical control structure in the direction of increasing stability, where the intentional process of reparameterization is itself dynamical. Subjects learned to oscillate pendulums held in the right and left hands such that the right hand frequency was twice that of the left (2:1 frequency lock). Over 12 learning sessions of 20 trials each, we interpreted the decreasing fluctuations in the frequency locking to be an index of the increasing concavity of the underlying potential, a measure of stability; the time required to achieve the 2: 1 pattern was interpreted as indexing the relaxation time of an intentional dynamic. Power spectral analyses of the phase velocity ratio exhibited two strategies for acquiring the interlimb movement pattern: (a) adding spectral peaks at integer multiples of the left hand frequency or (b) distributing power across many frequencies in a l/f-like manner. Results are discussed in terms of the promise of a dynamical approach to learning coordinated movements.     

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.     

Grammatical priming effects between pronouns and inflected verb forms

Summary Deciding on the lexical status of a word can be facilitated by a preceding, semantically related word. Three experiments are reported demonstrating a different kind of facilitation due to the grammatical relation between function words and content words in Serbo-Croatian. A pronoun facilitated or inhibited the lexical decision on a following verb depending on whether the person of the verb, as represented by its inflected ending, agreed with the person of the pronoun. Also, verbs primed subsequent pronouns but the pattern of results for the verbal priming of pronouns was markedly different from that for the pronominal priming of verbs. The results suggest that the organization of the internal lexicon is sensitive to grammatical relations as well as semantical relations between words.