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Biomedical subjects

V J Samar

Publications and source records attributed to V J Samar.

26 records · Page 2Linked to original sources
PubMed1985

Parafoveal attention in congenitally deaf and hearing young adults.

This reaction-time study compared the performance of 20 congenitally and profoundly deaf, and 20 hearing college students on a parafoveal stimulus detection task in which centrally presented prior cues varied in their informativeness about stimulus location. In one condition, subjects detected a parafoveally presented circle with no other information being present in the visual field. In another condition, spatially complex and task-irrelevant foveal information was present which the subjects were instructed to ignore. The results showed that although both deaf and hearing people utilized cues to direct attention to specific locations and had difficulty in ignoring foveal information, deaf people were more proficient in redirecting attention from one spatial location to another in the presence of irrelevant foveal information. These results suggest that differences exist in the development of attentional mechanisms in deaf and hearing people. Both groups showed an overall right visual-field advantage in stimulus detection which was attenuated when the irrelevant foveal information was present. These results suggest a left-hemisphere superiority for detection of parafoveally presented stimuli independent of cue informativeness for both groups.

Adult↗
PubMed1985

Acoustic dimensions of hearing-impaired speakers' intelligibility.

Regression and principal components analyses were employed to study the relationship between three measures of speech intelligibility and 12 segmental, prosodic, and hearing ability parameters in 20 severely to profoundly hearing-impaired speakers. Regression analyses on the original 12 parameters revealed that cognate pair voice onset time differences and mean sentence duration strongly predicted speech intelligibility based on readings of isolated word and contextual speech material. A principal components analysis derived four factors that accounted for the majority of the variance in the original 12 parameters. Subsequent regression analyses using the four factors as predictor variables revealed two factors with strong relationships to the speech intelligibility measures. One factor primarily reflected segmental production processes related to the temporal and spatial differentiation of phonemes, whereas the other factor reflected prosodic features and production stability. These results are consistent with prior research that suggests independent primary and secondary roles for segmental and prosodic speech characteristics, respectively, in determining intelligibility in severely to profoundly hearing-impaired speakers.

Adult↗
PubMed1984

Visual evoked-response components related to speechreading and spatial skills in hearing and hearing-impaired adults.

Averaged visual evoked responses (VER) to light flashes which varied systematically in brightness and predictability were collected from 24 hearing and 24 hearing-impaired adults. In addition, speechreading, abstract reasoning, and spatial relations tests were administered. Separate principal components analyses of the VERs were conducted on each group to replicate and extend our previous report of an early VER component (VF16) which reflected individual differences in the speechreading skills of hearing subjects. VF16 appeared in both analyses, confirming its replicability as a latent VER component. VF16 correlated with speechreading skill in hearing-impaired males (r = -.73), under stimulus conditions identical to those in our previous study. However, its correlations with speechreading skills in hearing subjects were not significant. VF16 also varied systematically with stimulus predictability and correlated with spatial ability in both groups only when the time of occurrence of the light flashes was predictable. These data tentatively suggest that VF16 is a VER correlate of individual differences in a psychologically dynamic process, perhaps involving expectancy, which may relate to the performance of hearing-impaired and hearing people in visually based communication or cognitive processing situations.

Adult↗
PubMed1983

Multidimensional influences of cerebral asymmetries on visual half-field asymmetries and cognitive skills.

Evoked potentials to laterally presented stimuli were collected from left and right tempero-parietal sites during performance of two visual half-field tasks, lexical decision, and line orientation discrimination. Reaction time and accuracy data were simultaneously collected. The behavioral data indicated the development of a right field advantage for the lexical decision task as a function of practice. A principal components analysis revealed three independent evoked potential components which displayed task-dependent hemispheric asymmetries. Multiple regression analyses revealed that visual half-field asymmetries in response accuracy were closely related to hemispheric asymmetries on several independent evoked response components. Subject's scores on independent tests of verbal reasoning and spatial relations were also found to be closely related to hemispheric asymmetry on several independent evoked response components. These data support a multidimensional concept of cerebral specialization. They also suggest that visual field asymmetries reflect the confluence of several underlying processes which have independent lateralization distributions across the population. In general, the results underscore the need for further research on the nature of the relationship between cerebral and perceptual asymmetries.

Adolescent↗
PubMed1983

Evoked potential and visual half-field evidence for task-dependent cerebral asymmetries in congenitally deaf adults.

Twelve congenitally deaf subjects participated in a visual half-field experiment under two conditions, lexical decision and line orientation discrimination. Reaction time, accuracy, and evoked potentials from left and right temporo-parietal sites were simultaneously obtained. The evoked potential data were analyzed using a principal components analysis followed by analysis of variance and multiple regression. Both the visual half-field and the evoked potential data produced evidence of task-dependent cerebral asymmetries. Individual differences in visual half-field asymmetries in accuracy and individual scores on three cognitive paper and pencil tests were strongly predicted by linear combinations of several independent hemispheric asymmetry variables derived from evoked potential component scores. The results suggest that cerebral specialization in congenitally deaf people is a complex, multidimensional phenomenon, and provide the first evidence for a direct relationship between cerebral asymmetry and cognitive performance in this population.

Adult↗
PubMed1983

Visual evoked-response correlates of speechreading performance in normal-hearing adults: a replication and factor analytic extension.

The relationship between the latency of the negative peak occurring at approximately 130 msec in the visual evoked-response (VER) and speechreading scores was investigated. A significant product-moment correlation of -.58 was obtained between the two measures, which confirmed the fundamental effect but was significantly weaker than that previously reported in the literature (-.90). Principal components analysis of the visual evoked-response waveforms revealed a previously undiscovered early VER component, statistically independent of the latency measure, which in combination with two other components predicted speechreading with a multiple correlation coefficient of .84. The potential significance of this new component for the study of individual differences in speechreading ability is discussed.

Adult↗
PubMed1983

Acoustic analysis of stutterers' fluent speech before and after therapy.

The speech of 14 stutterers was analyzed prior to and at the termination of a 5-week stuttering therapy program to examine the relationship between nine selected acoustic variables and stuttering frequency. Group analyses indicated that pre- to post-therapy changes in stuttering frequency were accompanied by mean changes in five of the nine acoustic variables, a finding which is consistent with previous literature. Correlational analyses indicated that only silence in the voiced stop consonant intervocalic interval (IVI) was significantly correlated with stuttering frequency prior to therapy (i.e., lower stuttering frequency values were associated with shorter durations of silence during the IVI). Furthermore, the degree of reduction in silence was positively correlated with the magnitude of reduction in stuttering frequency due to therapy. These findings suggest that silence in the IVI may reflect the operational status of some mechanism which may underlie disfluent speech.

Female↗