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Biomedical subjects

R D Easton

Publications and source records attributed to R D Easton.

17 recordsLinked to original sources
PubMed1997

Do vision and haptics share common representations? Implicit and explicit memory within and between modalities.

Previous assessments of verbal cross-modal priming have typically been conducted with the visual and auditory modalities. Within-modal priming is always found to be substantially larger than cross-modal priming, a finding that could reflect modality modularity, or alternatively, differences between the coding of visual and auditory verbal information (i.e., geometric vs. phonological). The present experiments assessed implicit and explicit memory within and between vision and haptics, where verbal information could be coded in geometric terms. Because haptic perception of words is sequential or letter-by-letter, experiments were also conducted to isolate the effects of simultaneous versus sequential processing from the manipulation of modality. Together, the results reveal no effects of modality change on implicit or explicit tests. The authors discuss representational similarities between vision and haptics as well as image mediation as possible explanations for the results.

Acoustic Stimulation↗
PubMed1996

Haptic cues for orientation and postural control in sighted and blind individuals.

Haptic cues from fingertip contact with a stable surface attenuate body sway in subjects even when the contact forces are too small to provide physical support of the body. We investigated how haptic cues derived from contact of a cane with a stationary surface at low force levels aids postural control in sighted and congenitally blind individuals. Five sighted (eyes closed) and five congenitally blind subjects maintained a tandem Romberg stance in five conditions: (1) no cane; (2,3) touch contact (< 2 N of applied force) while holding the cane in a vertical or slanted orientation; and (4,5) force contact (as much force as desired) in the vertical and slanted orientations. Touch contact of a cane at force levels below those necessary to provide significant physical stabilization was as effective as force contact in reducing postural sway in all subjects, compared to the no-cane condition. A slanted cane was far more effective in reducing postural sway than was a perpendicular cane. Cane use also decreased head displacement of sighted subjects far more than that of blind subjects. These results suggest that head movement control is linked to postural control through gaze stabilization reflexes in sighted subjects; such reflexes are absent in congenitally blind individuals and may account for their higher levels of head displacement.

Adult↗
PubMed1996

mtDNA variation in the Yanomami: evidence for additional New World founding lineages.

Native Americans have been classified into four founding haplogroups with as many as seven founding lineages based on mtDNA RFLPs and DNA sequence data. mtDNA analysis was completed for 83 Yanomami from eight villages in the Surucucu and Catrimani Plateau regions of Roraima in northwestern Brazil. Samples were typed for 15 polymorphic mtDNA sites (14 RFLP sites and 1 deletion site), and a subset was sequenced for both hypervariable regions of the mitochondrial D-loop. Substantial mitochondrial diversity was detected among the Yanomami, five of seven accepted founding haplotypes and three others were observed. Of the 83 samples, 4 (4.8%) were lineage B1, 1 (1.2%) was lineage B2, 31 (37.4%) were lineage C1, 29 (34.9%) were lineage C2, 2 (2.4%) were lineage D1, 6 (7.2%) were lineage D2, 7 (8.4%) were a haplotype we designated "X6," and 3 (3.6%) were a haplotype we designated "X7." Sequence analysis found 43 haplotypes in 50 samples. B2, X6, and X7 are previously unrecognized mitochondrial founding lineage types of Native Americans. The widespread distribution of these haplotypes in the New World and Asia provides support for declaring these lineages to be New World founding types.

Adult↗
PubMed1995

Object-array structure, frames of reference, and retrieval of spatial knowledge.

Experiments are reported that assessed the ability of people, without vision, to locate the positions of objects from imagined points of observation that are related to their actual position by rotational or translational components. Theoretical issues addressed were whether spatial relations stored in an object-to-object system are directly retrieved or whether retrieval is mediated by a body-centered coordinate system, and whether body-centered access involves a process of imaging updating of self-position. The results, with those of Rieser (1989), indicate that in the case of regularly structured object arrays, interobject relations are directly retrieved for the translation task, but for the rotation task, retrieval occurs by means of a body-centered coordinate system, requiring imagined body rotation. For irregularly structured arrays, access of interobject spatial structure occurs by means of a body-centered coordinate system for both translation and rotation tasks, requiring imagined body translation or rotation. Array regularity affected retrieval of spatial structure in terms of global shape of interobject relations and local object position within global shape.

Adult↗
PubMed1995

Wave collation visual speech display: design and evaluation.

The wave collation display is a pitch-synchronous, time-domain visual speech display. Collation processing maps the speech waveform into a planar array, condensing the waveform and making speech information, including pitch contour and formant transitions, salient. Evaluation included both analytic evaluation and training. Analytic evaluation was based on a perceptual sorting task using untrained subjects. Subjects sorted printed speech display tokens by visual similarity in a match-to-exemplar design. Stimuli included vowels, with single speaker, multiple speakers, and multiple phonemic contexts, and voiceless consonants. Results for untrained subjects ranged from 73% correct (consonants) and 71% correct (vowels) for single speaker tokens to 46% correct (multiple speaker vowels). For comparison, analytic evaluation using spectrograms was also performed for vowels with single and multiple speakers. Overall results were statistically equivalent to the collation display, with 76% correct (single speaker vowels) and 44% correct (multiple speakers). In the training component, four subjects were trained on collation display sorting tasks as above; after mastering these tasks, generalization to novel stimuli was tested. The tasks were mastered in a few hours, and generalization to novel tokens from a familiar speaker was nearly perfect; generalization to unfamiliar speakers was imperfect.

Color Perception↗
PubMed1992

Inherent problems of attempts to apply sonar and vibrotactile sensory aid technology to the perceptual needs of the blind.

A program of research dealing with two types of sensory aids for the blind--sonar and vibrotactile--is described. Rather than immediately assessing the aids in the mobility context, which has customarily been the case, the aids' capabilities are considered in terms of the major functions of vision, that is, the exteroceptive perception of objects, surfaces, and events of the environment, and the proprioceptive perception of the self, especially the self in relation to the environment. Although sonar aids function very well for localizing objects and for providing acoustic flow specifying self-movement, they do not provide high acuity pattern and shape information due to the long wavelength of ultrasound relative to light. This limitation is considered specifically with respect to the visual accomplishment of recovery of three-dimensional structure/motion from dynamic two-dimensional images. Vibrotactile sensory aids using optical imaging can deliver detailed pattern information to the skin and thus permit assessment of the extent to which a nonvisual system can mediate the recovery of structure problem. However, in even moderately cluttered or complicated environments the skin proves unable to resolve the amount of stimulation it receives vibrotactually. The limitations of sonar and vibrotactile sensory aids are discussed with respect to future sensory substitution efforts as well as their implications for understanding differences and similarities among the senses.

Blindness↗
PubMed1986

Effect of referent object familiarity on verbal learning in the sighted and the blind.

In a series of paired-associate tasks we investigate why some highly concrete nouns are easier to remember than other highly concrete nouns, even when such word attributes as imagery value are held constant. In Experiment 1 both the congenitally blind and the sighted remembered nouns with referents highly familiar to the blind better than nouns with referents of low familiarity to the blind. Although this effect was anticipated for the blind, it was unexpected for the sighted because the referents of low familiarity to the blind have been visually experienced by the sighted and are as easy for the sighted to image as the referents highly familiar to the blind. Experiments 2 through 5 explore why the extent to which the blind are familiar with an object should predict verbal learning for the sighted. As it turned out, referents that were familiar to the blind were also familiar to the sighted. After ruling out various alternative explanations we were able to conclude that it is the extent of perceptual experience with a noun's referent, irrespective of the modality through which the experience is acquired, that determines ease of verbal learning. Any theory that accounts for the concrete-noun effect must also be able to account for the effect of referent familiarity, and our results are discussed within this context.

Adult↗
PubMed1983

The effect of head movements on visual and auditory dominance.

Two experiments were performed to determine the effect of active auditory exploration (head movement) on visual and auditory dominance. In each experiment subjects located a small audio speaker unimodally or bimodally. On the bimodal trials a modality discordance was created by requiring prismatic viewing. Half the subjects in each experiment remained unaware of the discordance while the other half were informed that a prism was used, and its refracting properties were demonstrated. The second experiment differed from the first by allowing observers free head movement during target localization which was transduced and recorded electromechanically. The results indicated that knowledge of modality discordance greatly reduced visual bias of audition for observers with heads immobilized, but did not affect auditory bias of vision significantly. Observers permitted head movement but not provided with knowledge of discordance demonstrated visual bias which was substantially reduced from that found in the first experiment for no-knowledge subjects. Observers who were permitted head movement and provided with knowledge of discordance demonstrated no visual bias or auditory bias. Head movements were executed systematically, when permitted, and resulted in an increase in the precision of auditory localizations and a reduction in the biasing effect of vision. In contrast, head movement did not affect the precision of visual localizations. Results are discussed in terms of current hypotheses regarding perceptual dominance.

Attention↗
PubMed1978

A quantitative confirmation of visual capture of curvature.

An investigation was performed to quantify the experience of contour curvature formed under sensory discrepancy inspection conditions. N = 80 male and female undergraduates were used. Experimental Ss finger-tracked a horizontal straight edge while viewing limb movements through a curve inducing lens. Control Ss inspected the edge unimodally, either through vision (distorted) or proprioception. Rather than relying on verbal reports all Ss were required to match their impressions of contour shape with an adjustable metal curve. Findings indicated that (a) the mean impression of contour shape derived from discrepant visual and proprioceptive information was curved and did not differ from that derived from distorted visual information, (b) proprioceptive inspection alone resulted in accurate judgements of physical straightness, (c) response modality effects did not emerge, and (d) a manipulation designed to direct Ss attention to the left contour shape and during sensory discrepancy inspection did not affect mean curvature matches but created sizeable variability among matches. A sensory organization versus a selective processing interpretation of visual capture was discussed.

Attention↗
PubMed1976

An experimental analysis of the Chevreul pendulum illusion.

An investigation was performed, with the use of 60 male and female college students, to quantify the Chevreul pendulum illusory effect, the tendency of a small pendulum, when suspended from the hand and imaginatively concentrated upon, to oscillate seemingly of its own accord. By means of a time exposure photographic measurement technique, strong parametric influences of the pendulum's sinusoidal motion were isolated. It was found that the pendulum effect was enhanced when (a) attentional capacity remained undivided, (b) the amount of musculature used to suspend the pendulum was at a maximum, (c) oscillating visual and auditory external stimuli were present, and (d) females were Ss. In addition, the visual stimulus was found to be superior to its auditory counterpart. The relevance of ideomotor and visual capture interpretations of covert muscle processes in the pendulum illusion was discussed.

Attention↗
PubMed1976

Relation between optically induced and tracking-limb-movement curvature in a visual capture phenomenon.

Two experiments were conducted to help determine the nature of visual capture in the perception of curvature. If an individual finger-tracks a straight edge while viewing limb movements through a curve-inducing lens, the edge is reported to feel curved even though the finger is moving in a straight path. It has recently been demonstrated, however, that the finger actually tracks the straight edge through a curved path with the same orientation as the induced visual curve. In order to specify more completely the degree of relation between the visual and tracking (motor) curves the first experiment determined the fate of tracking limb-movement curvature when the eyes were closed. The second experiment determined whether curvature of tracking limb movement decreased as the magnitude of the visual curve was decreased. Results from both experiments supported the contention that curved tracking limb movement may mediate the visual and felt curves. The nature of the mechanism underlying felt curvature in visual capture was discussed.

Female↗
PubMed1975

Information processing analysis of the Chevreul pendulum illusion.

An information processing investigation was performed to quantify the Chevreul pendulum effect: the tendency of a small pendulum, when suspended from the hand and imaginatively concentrated on, to oscillate seemingly of its own accord. Using a time exposure photographic measurement technique, electronically automated visual and auditory imaginal prompts were presented to the subject during imaginal processing tasks. It was found that the pendulum effect was enhanced when vision of actual pendulum oscillations was permitted and visual or auditory spatially oscillating stimuli were present. Visual spatially oscillating stimuli were superior to their auditory counterparts. Results were discussed in terms of ideomotor and visual capture interpretations of signal and imaginal processing.

Adolescent↗