Biomedical subjects

J L Andreassi

Publications and source records attributed to J L Andreassi.

31 records · Page 2Linked to original sources

PubMed1982

Hemispheric sex differences in response to apparently moving stimuli as indicated by visual evoked potentials.

This research was designed to determine whether visual event related potentials (ERPs) recorded from over the two occipital hemispheres would indicate differential processing of apparently moving and stationary stimuli. Previous findings in the literature led us to consider a male-female comparison as part of our experimental design. Nine male and nine female subjects were screened for right-handedness and visual abilities (acuity, depth and phoria). Each participated in three experimental sessions over a three day period in which ERPs were recorded from O1 and O2 in response to stimuli presented in left, central and right visual fields. The main finding was that, for female subjects, right hemispheric derived ERPs were larger in amplitude than left hemisphere recordings for apparently moving stimuli presented centrally. Males showed no hemispheric amplitude differences. However, for male subjects, the left hemisphere ERP latencies to motion were longer than those recorded from over O2 with central visual field presentations. It was speculated that different attentional strategies in the two sexes led to the observed result.

Adolescent↗

PubMed1982

Visual evoked potentials under varied velocities of continuous and discrete apparent motion.

This experiment was undertaken to investigate the effects of different types and velocities of apparent motion on the Visual Evoked Potential (VEP). Central (Cz) recording site VEPs were obtained from four males and three females under seven conditions. Significant differences in terms of amplitude and latencies were found between continuous and discrete apparent motion at the Oz derivation only. Theoretical and cell system models describing separate cortical channels for processing continuous and discrete apparent motion were presented to account for the observed differences. The stationary condition produced a significantly shorter latency than all other conditions at Cz. In addition, discernable trends observed between central and occipital recording sites suggest the role of the occipital cortex as the primary processor of motion and for detecting differences in motion velocity.

Adult↗

PubMed1979

Monocular and binocular visual evoked potentials before and after cataract surgery.

Visual evoked cortical potentials (VEPs) were recorded from an individual with a mature cataract in one eye. Stimulation was both monocular and binocular and VEPs were obtained from three occipital scalp sites. Comparisons of recordings taken prior to cataract removal and after removal showed a dramatic increase in amplitude of potentials derived through stimulation of the affected eye. Slight differences in hemispheric amplitude prior to surgery suggest a greater degree of opacity in one portion of the affected lens.

Cataract↗

PubMed1976

Amplitude changes in the visual evoked cortical potential with backward masking.

A series of three experiments examined backward visual masking effects and visual evoked cortical potential correlates of such masking. In Experiment I, which was concerned with the effects of sequential sets of like stimuli (grids), it was found that when backward masking occurred, it was accompanied by decreased visual evoked potential (VEP) amplitudes. Experiment II replicated the first experiment using different stimuli (letter B's) and several new subjects. Again, backward masking was accompanied by decreased VEP amplitudes. In Experiment III, which examined the effects of sequential sets of unlike stimuli (B's and grids), it was found that when earlier stimuli differed in configuration from later stimuli, there was an absence of backward masking and VEP amplitude changes also failed to appear. Thus, when backward masking did not occur, no changes in the VEP were observed. The results are discussed in terms of interactions between excitatory and inhibitory activities produced at the visual cortex by the earlier and subsequently presented stimuli. Various concepts regarding the visual system mechanisms involved in backward masking, including integration and interruption hypotheses, may help to explain the complexity of findings obtained thus far in studies using VEP correlates of backward visual masking.

Evoked Potentials↗

PubMed1976

Hypnotic suggestion of stimulus change and visual cortical evoked potential.

Two experiments were conducted to determine whether the hypnotic suggestion of stimulus intensity change would affect the physical parameters (latencies, amplitudes) of the visual cortical evoked potential. Stimulus intensity was kept constant as visual cortical evoked potentials were measured under conditions in which it was suggested that stimuli were "bright" or "dim". The results of both experiments led to the conclusion that, under the present condition, hypnotic suggestion of stimulus intensity change did not result in changes in visual cortical evoked potentials.

Electrophysiology↗

PubMed1975