Biomedical subjects

S Christman

Publications and source records attributed to S Christman.

11 recordsLinked to original sources

PubMed1998

The role of hemispheric activation in person perception: evidence for an attentional focus model.

Two studies assessed the role of hemispheric activation in person perception. Results of Study 1 supported an attentional focus model of hemispheric differences in person perception as opposed to a stereotyping/individuating model. Relative to left hemisphere-activated participants, right hemisphere-activated participants made more individuating judgments and engaged in more trait level stereotyping, whereas left hemisphere-activated participants engaged in more global stereotyping. In Study 2, greater individuation by participants under higher levels of motivation and ability was shown to be mediated by relatively greater right hemisphere activation. Results of both studies are interpreted in terms of an attentional focus model of person perception. Implications for dual process models of social perception are also discussed.

Adult↗

PubMed1998

Effects of mood on color perception as a function of dimensions of valence and arousal.

Effect of observers' emotional state on color discrimination was examined. Observers in happy (n = 18) versus sad (n = 18) emotional states, as induced by Eich and Metcalfe's 1989 procedure, were faster at discriminating high versus low arousal colors, respectively. Emotional state of observers had no effect on processing colors differing in valence.

Affect↗

PubMed1997

Lateral biases in aesthetic preferences: pictorial dimensions and neural mechanisms.

Observers often prefer one orientation of a stimulus over its mirror image; these lateral biases are assumed to reflect aspects of the observer's neural organisation. However, the precise dimensions of pictorial organisation that influence these preferences, as well as the underlying neural mechanisms, are not clear. The present experiments addressed these issues by employing a stimulus set allowing for a factorial combination of three dimensions of pictorial organisation: Weight, Interest, and Directionality. Experiments 1 and 2 found that subjects exhibited robust and consistent preferences for stimuli with left-to-right directionality, especially for stimuli with left-biased interest; right-biased interest eliminated the preference for left-to-right directionality. The dimension of weight had little effect. Inter-task correlations from Experiment 3 suggested that this preference for left-to-right directionality (i) reflects a stable, underlying directional bias in perceptuo-motor processing, and (ii) is not related to individual differences in hemispheric activation.

Journal Article↗

PubMed1993

Handedness in musicians: bimanual constraints on performance.

Handedness in musicians was examined in terms of the relative roles of the hands in bimanual motor activity involved in instrumental performance. Musicians playing instruments requiring temporally integrated (e.g., strings and wood-winds), as opposed to independent (e.g., keyboard instruments), bimanual motor activity were found to exhibit weaker degrees of handedness. There were no significant differences between groups in direction of handedness. Results are interpreted in terms of greater bilateral hemispheric integration and control of fine motor movements among subjects exhibiting mixed-handedness.

Brain↗

PubMed1993

Hemispheric differences in the interference among components of compound gratings.

The relationship between local/global and high/low spatial-frequency processing in hemispheric asymmetries was explored. Subjects were required to judge the orientation of a high- or low-spatial-frequency component of a compound grating presented in the left visual field (LVF) or right visual field (RVF). In Experiment 1, attention was focused on one or the other component. A signal detection analysis indicated that sensitivity (d') to the high-spatial-frequency target was reduced more by the presence of the low-spatial-frequency component when both were presented in the LVF rather than in the RVF. In Experiment 2, subjects determined whether a target orientation was present, independent of spatial frequency at only a single level (i.e., at the high- or low-spatial-frequency level), as opposed to both or neither level. An RVF/LH (left hemisphere) advantage was found when the decision was based on the orientation of the high-frequency component. The asymmetrical influence of visual field of presentation and spatial frequency upon sensitivity is discussed in terms of hemispheric differences in the magnitude of inhibition between spatial-frequency channels and in the role of transient channel activity to capture and direct higher order attentional processes.

Brain↗

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

Hemispheric asymmetry in the processing of absolute versus relative spatial frequency.

Observers indicated whether a stimulus presented to one visual field or the other consisted of two sine-wave gratings (the baseline stimulus) or those same two gratings with the addition of a 2 cycle per degree (cpd) component. When the absolute spatial frequencies of the baseline stimulus were low (0.5 and 1.0 cpd), there was a left visual field-right hemisphere (LVF-RH) advantage in reaction time (RT) to respond to the baseline stimulus which disappeared when the 2 cpd component was added (i.e., the stimulus consisted of 0.5, 1.0, and 2.0 cpd components). When the absolute spatial frequencies of the baseline stimulus were moderate to high (4.0 and 8.0 cpd), a right visual field-left hemisphere advantage in RT to respond to the baseline stimulus approached significance and shifted to a significant LVF-RH advantage when the 2 cpd component was added (i.e., the stimulus consisted of 2.0, 4.0, and 8.0 cpd components. That is, adding the same 2 cpd component caused opposite shifts in visual laterality depending on whether 2 cpd was a relatively high or relatively low frequency compared to the baseline.

Dominance, Cerebral↗

PubMed1990

Effects of luminance and blur on hemispheric asymmetries in temporal integration.

A task involving temporal integration of form was employed to examine the effects of input characteristics on hemispheric asymmetries. In Experiment 1, decreases in luminance produced greater improvement of right hemisphere (RH) performance. In Experiment 2, dioptric blur produced greater impairment of left hemisphere (LH) performance. The results suggest that spatial frequencies below nine cycles per degree are processed more efficiently in the RH. In Experiment 3, effects of input characteristics on hemispheric asymmetry were found to be dependent on the spatial frequencies required for processing by task demands, as mediated by interflash interval (IFI) duration. Increased blur produced greater impairment of LH performance at short IFI duration; at a longer IFI duration, however, increased blur produced equal impairment of RH and LH performance.

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

Temporal integration of form as a function of subject handedness and retinal locus of presentation.

Two experiments are reported examining differences in perceptual processing as a function of subject handedness. Experiment 1 compared performance in the left vs right visual fields of right- vs left-handed subjects. Only right-handed subjects exhibited an interaction of visual field with spatial frequency (as mediated by interflash interval), suggesting that left-handers are not differentially lateralized for high vs low spatial frequency processing. Experiment 2 examined foveal performance in left-handers vs right-handers with or without familial sinistrality. Subjects with personal or familial sinistrality exhibited superior performance when the processing of low frequencies was required, suggesting that sinistrality may confer an advantage in the processing of lower spatial frequencies.

Adult↗

PubMed1989

Perceptual characteristics in visual laterality research.

Visual laterality experiments from the last three decades are reviewed. The criterion for inclusion was the independent manipulation within a constant task paradigm of one or more of the following perceptual parameters: retinal eccentricity, stimulus size, luminance, contrast, blurring/degradation, and exposure duration. These results are discussed in light of a model of hemispheric lateralization based on asymmetries in the processing of visual spatial frequency.

Attention↗