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Biomedical subjects

M T Turvey

Publications and source records attributed to M T Turvey.

At least 109 records · Page 6Linked to original sources
PubMed1989

'Clock' and 'motor' components in absolute coordination of rhythmic movements.

Human subjects swung, through motions at the two wrists, hand-held pendulums of variable mass and length. Within a pair, the two pendulums could be of the same or different magnitude. The subjects were required to produce a coordinated state in which the two rhythmic units oscillated at a single common period. Fifty-four conditions of absolute coordination, that is, 54 different pairs of wrist-pendulum systems, were investigated for each of three subjects in the course of six sessions. Each condition of absolute coordination was conducted in the out of phase mode and at the single most comfortable period. The period variances of the right and left systems in the 162 instances of absolute coordination were analysed according to a method that assumes that a timekeeper function and a motor implementation function contribute independently to the variance in the periodic timing of a rhythmic movement. The major findings were that in absolute coordination: (a) a system's 'motor' variance, but not its 'clock' variance, depended on the deviation of the period of absolute coordination tau from the system's characteristic period; (b) right and left 'clock' variances were related and (c) neither the 'motor' variances nor the 'clock' variances were affected by deviations in the mean phase relation from 180 degrees. The results were discussed in terms of their implications for interpreting von Holst's notions of maintenance tendency and magnetic effect and, more generally, the neural and dynamical basis of absolute coordination.

Adult↗
PubMed1989

Perceiving extents of rods by wielding: haptic diagonalization and decomposition of the inertia tensor.

We report two experiments on the length-perception capabilities of the hand-related haptic subsystem. On each trial, a visually occluded rod was wielded by the subject at a position intermediate between its two ends. The position was either 1/2 or 3/4 of the rod's length. On two-thirds of the trials, a weight was attached to the rod at a point either above or below its center of gravity and not coincident with the hand's position. In Experiment 1, the subject's task was to perceive the distance reachable with the portion of the rod extending beyond the position of the grasp. In the second experiment, the subject's task was to perceive the distance reachable with the entire rod if it were held at its proximal end. In Experiment 1, perceived reaching distance was a function of the moment of inertia of the amount of rod forward of the grasp about an axis through the proximal end of the rod segment. In Experiment 2, perceived reaching distance was a function of the moment of inertia of the entire rod about the given axis of rotation intermediate between the rod's ends. The results are discussed in terms of (a) the notion of smart perceptual instruments capitalizing on invariant properties of the inertia tensor and (b) how the haptic decomposition of moments of inertia follows the principle of equivalence of forces.

Adult↗
PubMed1989

An ecological analysis of knowing by wielding.

The ecological approach to perception, as developed by James Gibson, is described and applied to how one knows, by means of the haptic perceptual system, various properties of hand-held objects. Four sets of experiments are reviewed in which subjects reported on the extent, orientation, shape, and fractional components of unseen objects wielded freely. For each task, an invariant specific to the object property in question is identified in the structured arrays of rotational moments and strains produced by the act of wielding. Results are discussed in relation to the concepts of attention and stimulation, as reformulated by the ecological approach, and the general theory of perception as information pickup.

Attention↗
PubMed1988

On the time allometry of co-ordinated rhythmic movements.

The focus is the power formulae relating periodic time in terrestrial locomotion and flight to mass and length. The periodic timing of limbs and wings oscillating comfortably in absolute co-ordination is viewed as the characteristic period tau 0 of a system in which the free, undamped oscillatory motion of a point mass m at a distance l from a fixed axis does work against two conservative forces. These forces are in the form of gravity g acting on the point mass and a spring of stiffness k acting at a distance b from the axis. The system's characteristic period can be expressed most simply as: tau 0 = 2 pi [ml2/(mlg + kb2)]1/2. In the biological instantiation of this hybrid mass-spring/simple pendulum system, muscular and other tissues function as the spring that elastically stores and releases mechanical energy. Regular oscillations are brought about and sustained by a muscular driving force that ordinarily is close to resonance. The resultant dynamical regime--basically, raising and lowering a mass at regular intervals with respect to gravity--is referred to as the pendular clocking mode of movement organization. The mode is investigated comfortably at a common period and a fixed phase. In absolute co-ordination, two wrist-pendulum systems can be interpreted physically as a virtual single system. The evidence suggests that the scalings of the periodic times of such systems to mass and to length follow directly from the dynamical properties inherent in the resonance equation of the pendular clocking mode. Recourse to biological constants to rationalize the time scale is unnecessary. Experiments on human wrist-pendular activity and detailed analyses of the mass and length dependencies of the locomotory cycle times of quadrupeds, large birds, small passerines, hummingbirds, and insects are performed with respect to the dynamical properties predicted for systems in the pendular clocking mode. The major conclusion is that all the time scales of terrestrial in locomotory time allometries follow systematically from differences in the length scale and differences in the relation of mass to length.

Animals↗
PubMed1988

Maintenance tendency in co-ordinated rhythmic movements: relative fluctuations and phase.

Evidence from the oscillatory behavior of fish fins and the crayfish swimmeret system suggests that local rhythmic-pattern generators preserve their characteristic properties over the various locomotory co-ordinations in which they participate. This maintenance tendency, as von Holst termed it, was investigated in an experiment in which human subjects swung, through motions at the wrists, hand-held pendulums of variable mass and length. In the experiment (comprising six sessions over 21 months with the same three subjects) the context for the maintenance tendency was steady-state absolute co-ordination: two rhythmic units oscillating at a single, common period and at a bounded phase relation. The experimental methodology permitted systematic control of (a) the characteristic periods of the individual rhythmic units and (b) the deviations from these periods. Relative fluctuations in periodic timing and amplitude were least when a rhythmic unit's period in absolute co-ordination approximated its characteristic period and increased with departures from the characteristic period. Rates of increase in timing fluctuations were approximately the same for deviations on either side of the characteristic period; the rate of increase in spacing fluctuations was substantially greater for the range in which periods were less than the characteristic period. The phase relation between two co-ordinated rhythmic movement units in absolute co-ordination depended on the difference between their characteristic periods. The intended phase relation of 180 degrees was attained only when the characteristic periods were identical. When the characteristic periods differed, the departure from 180 degrees increased systematically with the difference. The fluctuation results are discussed in terms of the relation between relaxation and harmonic dynamics in producing rhythmic movements, with particular emphasis on the harmonic tuning of relaxation oscillations. The phase results are discussed in terms of whether or not the very many stable phase relations in absolute co-ordination are reflective of the nervous system or of differences in response latencies in left and right muscle systems induced by different degrees of inertial compensation.

Adult↗
PubMed1988

Haptically perceiving the distances reachable with hand-held objects.

Nine experiments are reported on the ability of people to perceive the distances reachable with hand-held rods that they could wield by movements about the wrist but not see. An observed linear relation between perceived and actual reaching distances with the rods held at one end was found to be unaffected by the density of the rods, the direction relative to the body in which they were wielded, and the frequency at which they were wielded. Manipulating (a) the position of an attached weight on an otherwise uniformly dense rod and (b) where a rod was grasped revealed that perceived reaching distance was governed by the principal moment(s) of inertia (I) of the hand-rod system about the axis of rotation. This dependency on moment of inertia (I) was found to hold even when the reaching distance was limited to the length of rod extending beyond an intermediate grasp. An account is given of the haptic subsystem (hand-muscles-joints-nerves) as a smart perceptual instrument in the Runeson (1977) sense, characterizable by an operator equation in which one operator functionally diagonalizes the inertia and strain tensors. Attunement to the invariants of the inertia tensor over major physical transformations may be the defining property of the haptic subsystem. This property is discussed from the Gibsonian (ecological) perspectives of information as invariants over transformations and of intentions as extraordinary constraints on natural law.

Adult↗
PubMed1988

Low-constraint facilitation in lexical decision with single-word contexts.

Single-word, low-constraint adjective contexts were used to "prime" lexical decision to noun targets in Serbo-Croat. Semantically congruent situations consisted of adjective-noun pairs that were not highly predictable but were nonetheless plausible (e.g., GOOD-AUNT). Semantically incongruent situations used pairs that were implausible (e.g., SLOW-COAT). All adjective-noun pairs were grammatically congruent and were compared with a neutral XXX baseline. In Experiment 1, at a stimulus onset asynchrony of 300 ms, congruous situations showed 59 ms of facilitation while incongruous situations did not differ from the baseline. The same pattern was repeated in Experiment 2, at a stimulus onset asynchrony of 800 ms. Congruous situations were facilitated 67 ms. Results are discussed in terms of a message-level coherence check in Forster's (1979) model of autonomous levels of language processing.

Cues↗
PubMed1986

Hemispheric asymmetries in phonological processing.

In Serbo-Croat, lexical decision to phonologically bivalent letter strings is slowed relative to their phonologically unique counterparts. This feature was exploited in order to assess the linguistic capacity of the two hemispheres. Lexical decision to laterally presented words and pseudowords revealed a right visual field advantage for both males and females in words and pseudowords. But the demands of phonological processing were not met in the same way by the two hemispheres, the two hemispheres did not respond in the same way in the two sexes, and the pattern of these differences was opposite for words and pseudowords.

Adolescent↗
PubMed1986

Fluctuations and phase symmetry in coordinated rhythmic movements.

Pendular, clocking movements typify mammalian terrestrial locomotion. They can be investigated with a procedure in which people swing hand-held pendulums at the wrists, comfortably and rhythmically. Pendular, clocking behavior was examined for in-phase and out-of-phase coordinations. The periodic timing and powering of rhythmic movements in the comfort state follow from different laws (Kugler & Turvey, 1986). One law guides the assembling of the reference frame for "clocking." Another law guides the assembling of the muscular, escapement processes determining the cycle energy. Wing and Kristofferson's (1973) method for parsing periodic-timing variance into independent "clock" and "motor" sources was applied. Mean periodicity was unaffected by phase. "Clock" fluctuations, however, were larger out of phase than in phase. "Motor" fluctuations were indifferent to phase but reflected the departures of individual wrist-pendulum systems from their preferred periods. It appears that an intended phase relation is realized as a constraint on "clock" states. These states are more stable under the in-phase constraint than under the out-of-phase constraint.

Biophysical Phenomena↗
PubMed1985

Effects of phonological ambiguity on beginning readers of Serbo-Croatian.

Third- and fifth-grade Yugoslavian children rapidly named familiar words and unfamiliar pseudowords that were written either in the Roman alphabet or in the Cyrillic alphabet and that were either phonologically ambiguous or not. Phonological ambiguity was produced by using letter strings that, when transcribed in Roman or when transcribed in Cyrillic, contained one or more ambiguous characters. Ambiguous characters are those letters shared by the two alphabets that receive different phonemic interpretations in the two alphabets. The controls for phonologically ambiguous words were the same words in their alternative, nonambiguous alphabetic transcription. Consistent with previous experiments on adults, the phonologically ambiguous form of a word or pseudoword was named much more slowly than the phonologically unambiguous form. For children who were equally proficient in both Roman and Cyrillic, the effect of phonological ambiguity was greater as children named letter strings faster. If it can be assumed that reading fluency correlates with naming latency, then it can be argued that the better beginning reader is more phonologically analytic.

Child↗
PubMed1985

Grammatical priming of inflected nouns by the gender of possessive adjectives.

Two experiments examined the effect on lexical decision times for inflected Serbo-Croatian nouns when the nouns were preceded by possessive adjectives (my, your, our). For any given pairing the possessive adjective and the noun agreed always in number (singular) and case (nominative) but only agreed half of the time in gender (masculine or feminine). Lexical decisions were faster when the noun targets were of the same gender as their primes. This gender congruency/incongruency effect was shown to hold whether the inflections of the adjective and noun were the same (as is the case for typical Serbo-Croatian nouns) or different (as is the case for atypical Serbo-Croatian nouns). The results are discussed in terms of a postlexical influence of grammatical processing on the recognition of individual words.

Adult↗
PubMed1985

A note on the natural basis of action categories: the catching distance of mantids.

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.

Journal Article↗
PubMed1984

A comment on equating information with symbol strings.

Symbol strings are advanced as the informational basis for many biological, physiological, and psychological phenomena. The role ascribed to them is that of indicating or directing states of affairs. Pattee has suggested that nature exploits information in this quasi-linguistic sense sparingly, that symbol strings are limited in detail, and that their relation to dynamics is one of complementation. A different, nonsymbolic view of information that addresses how animals can guide their locomotion in cluttered surroundings has been pursued by Gibson. It has considerable generality: information is low-dimensional qualitative properties of low-energy fields, lawfully generated by properties of systems and surround. It is argued that in the absence of information in Gibson's specificational sense, information in the indicational-injunctional sense is ineffective, and it is suggested that perplexities about the selective content of symbol strings may be resolved by a thoroughgoing understanding of Gibsonian information.

Animals↗