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Biomedical subjects

J B Hellige

Publications and source records attributed to J B Hellige.

At least 19 recordsLinked to original sources
PubMed1992

Visual hemispheric asymmetries depend on which spatial frequencies are task relevant.

Observers classified sine-wave and square-wave gratings on the basis of fundamental frequency (Are the bars wide or narrow?) or on the basis of higher harmonic frequencies (Are the bars sharp or fuzzy?). Stimuli were presented in either the left (LVF) or right (RVF) visual field. When the classification was made on the basis of the fundamental frequencies (1 or 3 c/deg), there was a LVF/right hemisphere advantage. However, when the classification was on the basis of a sharp/fuzzy distinction which involved searching for the higher harmonic frequencies, then a RVF/left hemisphere advantage was found.

Adult↗
PubMed1991

Perceptual reference frames and visual field asymmetry for verbal processing.

Two experiments investigated the role of perceptual reference frames in producing visual field asymmetries for the recognition of consonant-vowel-consonant (CVC) nonsense syllables. In an upright stimulus display condition, both quantitative and qualitative visual field asymmetries replicated those obtained in earlier studies of CVC identification. When the stimulus displays were rotated 90 degrees clockwise or counterclockwise, there were no effects of presenting the CVC in relative LVF vs relative RVF stimulus locations. The contrast between results in the upright and rotated stimulus display conditions indicates that the LVF/RVF differences in the upright displays are attributable to the position of the CVC relative to the fovea, rather than relative to the perceptual reference frame. This finding is consistent with the interpretation that LVF/RVF differences in the upright condition are attributable to hemispheric differences in the processing of linguistic/phonetic information.

Adult↗
PubMed1990

Effects of stimulus degradation on letter-matching performance of left and right hemispheric stroke patients.

Performance on a letter-matching task involving conditions of perceptual degradation was tested on 18 Right CVA patients, 18 Left CVA patients and 18 control subjects. Letter stimuli were presented in three conditions: Clear, Line-Masked, and Blurred. Subjects judged whether two letters of a pair were the same in name or different in name. Right CVA patients performed significantly less accurately than did Left CVA patients and control subjects when letters were perceptually degraded with a line mask overlay or by blurring. No significant differences were found between the two patients groups when the letters were presented without perceptual degradation (the Clear condition), but both patient groups were significantly less accurate than control subjects. The results are similar to findings reported in visual half-field studies with neurologically normal subjects and indicate right-hemisphere superiority for the processing of perceptually degraded visual information.

Adult↗
PubMed1990

Hemispheric differences are found in the identification, but not the detection, of low versus high spatial frequencies.

The processing of sine-wave gratings presented to the left and right visual fields was examined in four experiments. Subjects were required either to detect the presence of a grating (Experiments 1 and 2) or to identify the spatial frequency of a grating (Experiments 3 and 4). Orthogonally to this, the stimuli were presented either at threshold levels of contrast (Experiments 1 and 3) or at suprathreshold levels (Experiments 2 and 4). Visual field and spatial frequency interacted when the task required identification of spatial frequency, but not when it required only stimulus detection. Regardless of contrast level (threshold, suprathreshold), high-frequency gratings were identified more readily in the right visual field (left hemisphere), whereas low-frequency gratings showed no visual field difference (Experiment 3) or were identified more readily in the left visual field (right hemisphere) (Experiment 4). Thus, hemispheric asymmetries in the processing of spatial frequencies depend on the task. These results support Sergent's (1982) spatial frequency hypothesis, but only when the computational demands of the task exceed those required for the simple detection of the stimuli.

Adult↗
PubMed1989

Stimulus intensity, attentional instructions, and the ear advantage during dichotic listening.

The present experiment was designed to investigate the effects of the following two variables on the identification of dichotically presented CV syllables: (1) the relative difference in intensity levels of the stimuli presented to the two ears and (2) the instructions to attend to both ears or to focus attention on one ear. As expected for a verbal task, more CV's were identified from the right ear than from the left ear. Furthermore, identification of stimuli presented to one ear improved when (1) those stimuli were relatively higher in volume than the stimuli presented to the other ear and (2) when subjects were instructed to focus attention on only that ear rather than distribute attention across both ears. Of particular importance is the finding that the effects of relative stimulus intensity are the same under conditions of focused attention as under conditions of divided attention. This finding is inconsistent with an attention explantation of the relative intensity effects. Instead, the results are consistent with a model of dichotic listening in which ear of stimulus presentation and relative stimulus intensity influence a perceptual stage of information processing and attentional instructions influence a subsequent response selection stage.

Adult↗
PubMed1989

Interhemispheric interaction when both hemispheres have access to the same stimulus information.

Right-handed Ss identified consonant-vowel-consonant (CVC) nonsense syllables presented tachistoscopically. The CVC on each trial was presented to the left visual field-right hemisphere (LVF-RH), to the right visual field-left hemisphere (RVF-LH), or the same CVC was presented to both visual fields (bilateral presentation). When recognition was incorrect, the pattern of errors was qualitatively different on LVF-RH and RVF-LH trials, suggesting that each cerebral hemisphere has its own preferred mode of processing the CVC stimuli. The qualitative pattern of errors on bilateral trials was identical to that obtained on LVF-RH trials. The bilateral results are described well by a model that assumes the mode of processing characteristic of the RH dominates on bilateral trials but is applied to both the LVF-RH and RVF-LH stimuli.

Adult↗
PubMed1989

Categorization versus distance: hemispheric differences for processing spatial information.

It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision. The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation.

Adult↗
PubMed1988

Processing from LVF, RVF and BILATERAL presentations: examinations of metacontrol and interhemispheric interaction.

Observers indicated whether two successively presented drawings of faces were identical or differed in one feature (hair, eyes, mouth, jaw). The first face of each pair was presented at the fixation point and the second was presented to the left visual field-right hemisphere (LVF-RH), right visual field-left hemisphere (RVF-LH), or to both visual fields simultaneously (BILATERAL). On DIFFERENT trials the RT of correct responses depended on which feature differed and the pattern of feature location effects was significantly different on LVF-RH and RVF-LH trials. On BILATERAL trials the feature location effect was identical to that obtained on RVF-LH trials and significantly different from that obtained on LVF-RH trials. In addition, the percentage of errors and RT of correct responses were both higher on BILATERAL trials than on unilateral trials. Implications of these results are considered for the concept of "metacontrol" in neurologically normal humans and for models of interhemispheric interaction.

Attention↗
PubMed1988

Multitask investigation of individual differences in hemispheric asymmetry.

Right-handed subjects (N = 120) participated in four different laterality tasks designed to measure aspects of cerebral hemisphere asymmetry: identification of dichotically presented consonant-vowel syllables (CVs), examination of the effects of concurrent repetition of CVs and concurrent anagram solution on finger-tapping by the right and left hands, lateralized identification of CVs presented tachistoscopically to the left and right visual fields, and left/right biases on a free-vision face task involving judgments of emotion. Ear differences in the dichotic listening task were related to the pattern of lateralized interference in the dual-task finger-tapping paradigm. There were no other significant relations between pairs of tasks, but when the present results are considered in the light of other recent experiments, there appears to be a relation between lateral bias on the free-vision face task and visual field differences in tachistoscopic identification. The pattern of results has implications for hypothesized individual differences among right-handers in cerebral dominance for verbal processes, input pathway dominance, and asymmetric arousal of the two cerebral hemispheres.

Adult↗
PubMed1987

Effects of blurring and stimulus size on the lateralized processing of nonverbal stimuli.

Right-handed subjects indicated whether two novel, nonlinguistic stimuli were physically identical or not. In Experiment 1 blurring these stimuli impaired performance when stimuli were projected to the right visual field but not when stimuli were projected to the left visual field. This lateralized effect of blurring is similar to earlier findings in letter-matching experiments and indicates that such effects do not depend on hemispheric differences in verbal mediation. Experiment 2 examined the lateralized effects of stimulus size using the same task as Experiment 1. The pattern of results from this experiment suggests that both visual spatial frequency and stimulus perceptibility contribute to interactions of stimulus clarity and visual field and that neither factor by itself may be the sole determinant of the lateralized effects of input variables.

Adult↗
PubMed1986

Lateralized effects of blurring: a test of the visual spatial frequency model of cerebral hemisphere asymmetry.

In a Physical Identity letter comparison task, blurring the stimuli impaired performance when stimuli were projected to the right visual field but not when stimuli were projected to the left visual field. Whether this effect was obtained for response accuracy or for reaction time of correct responses depended on whether the stimuli were difficult or easy to classify. In two experiments it is shown that when the classification task is so difficult that the error rates are high, the Stimulus Clarity x Visual Field interaction is restricted to response accuracy measures. When the classification task is so easy that the error rates are low in all conditions, the critical interaction is restricted to reaction time of correct responses. The results are consistent with the hypothesis that the left and right hemispheres are biased toward efficient processing of higher and lower ranges of visual spatial frequency, respectively.

Biophysical Phenomena↗
PubMed1986

Lateralized interference in finger tapping: comparisons of rate and variability measures under speed and consistency tapping instructions.

Forty right-handed college subjects tapped with and without a verbal task under two instructional conditions (tap as quickly as possible vs. tap as consistently as possible) and two levels of verbal production (silent vs. aloud). The tapping task consisted of the alternate tapping of two keys with the index finger of the left vs. right hands, while the verbal task was anagram solution. Three rate and four variability measures of tapping performance were evaluated in the identification of lateralized interference. The results indicate that reliable lateralized interference, more right-hand than left-hand tapping disruption, was observed only for variability measures under instructions to tap as consistently as possible. Furthermore, only one of these variability measures was sensitive to an increase in lateralized interference produced by verbal production. Because of the limited demonstration of verbal laterality effects with the two-key tapping procedure in this study, conclusions suggest that the simpler manual task of repetitive tapping of one key should be viewed as the method of choice in future dual-task studies.

Female↗
PubMed1986

Visual laterality and the acuity gradient: potential artifacts and control procedures.

As visual stimuli are moved away from the fixation point toward either side, perceptibility falls off rapidly. This acuity gradient can influence visual half-field differences if the two sides (or ends) of a stimulus do not provide equal amounts of task-relevant information. In general, performance should be better in the visual field with the more informative side of the stimulus closer to the fixation point. Kirsner and Schwartz (1986, Brain and Cognition, 5, 354-361) discuss implications for experiments using words. The present article considers the assumptions involved in an explanation of visual half-field differences in terms of the visual acuity gradient and offers guidelines for the design of experiments using letters, faces (and other nonverbal stimuli), and words. Special attention is given to the interpretation of Visual Field X Task Variable interactions and to the use of words with letters arranged vertically. It is concluded that, with sufficient care in their design and interpretation, visual laterality experiments are an important converging operation for the study of cerebral hemisphere asymmetry.

Face↗
PubMed1986

Role of input factors in visual-field asymmetries.

This paper examines the implications of lateral tachistoscopic presentation of information for the processing efficiency of the intact cerebral hemispheres. Considering that the understanding of the processes underlying the particular competences of each hemisphere may require, as a preliminary step, the specification of the characteristics of the input on which the brain operates, anatomical, physiological, and psychophysical consequences of briefly stimulating the retinal periphery for the representation of information in the brain are outlined, with special reference to the spatial-frequency spectral composition of the stimuli. Retinal eccentricity and brief exposure duration converge to making the representation of information qualitatively different from the information that the brain normally operates on, which constrains the interpretation of findings with respect to the normal functions of the cerebral hemispheres. A review and discussion of empirical findings relevant to these issues suggest that manipulation of procedural variables may differentially affect the processing efficiency of the cerebral hemispheres and indicate that a given pattern of visual-field asymmetry may be overdetermined by a multitude of variables interacting in complex ways.

Discrimination Learning↗
PubMed1986

Role of task factors in visual field asymmetries.

Any tachistoscopic study of cerebral hemisphere asymmetry imposes a variety of task demands on the participants, ranging from demands imposed by specific viewing conditions to demands imposed by response output requirements. The present article discusses the role of several task factors that influence processing after the initial reception of the stimulus input, suggests a theoretical rationale for some of the effects of these task factors, and considers implications for future studies of visual laterality. The task factors discussed include both those that are relevant for minimizing artifacts that have nothing to do with hemispheric asymmetry and those that are relevant for interpreting hemispheric asymmetry in terms of specific perceptual and cognitive processes.

Attention↗
PubMed1979

Figural relationship effects and mechanisms of visual masking.

In each of three visual pattern masking experiments, four curved letters (C, O, Q, S) and four angular letters (E, I, L, T) served as targets preceded or followed by either a curved mask (Q,S, and C superimposed) or an angular mask (T and E superimposed). With a dark fixation and interstimulus interval field and target-mask engergies that produce clearly identifiable targets, the following figural relationship effects were found. At stimulus onset asynchronies (SOAs) from 0 to 20 msec (in both forward and backward masking), target recognition was more accurate when targets and masks overlapped exactly (same features) than when they did not (different features). At backward masking SOAs beyond 20 msec, this pattern was reversed, but there was no such reversal in forward masking. Such results indicate that the dominant mechanism of masking at SOAs from 0 to 20 msec is luminance summation over time but that luminance summation gives way to feature-specific interference at longer SOAs. Subsequent experiments demonstrate that (a) luminance summation effects are reduced by using bright fixation and interstimulus fields and (b) feature-specific interference is eliminated by using low-energy (and, therefore, less than perfectly identifiable) targets and masks.

Adult↗