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Biomedical subjects

L G Gawryszewski

Publications and source records attributed to L G Gawryszewski.

11 recordsLinked to original sources
PubMed1998

Gap effect and reaction time distribution: simple vs choice manual responses.

It is well known that saccadic reaction times (SRT) are reduced when the target is preceded by the offset of the fixation point (FP)--the gap effect. Some authors have proposed that the FP offset also allows the saccadic system to generate a separate population of SRT, the express saccades. Nevertheless, there is no agreement as to whether the gap effect and express responses are also present for manual reaction times (MRT). We tested the gap effect and the MRT distribution in two different conditions, i.e., simple and choice MRT. In the choice MRT condition, subjects need to identify the side of the stimulus and to select the appropriate response, while in the simple MRT these stages are not necessary. We report that the gap effect was present in both conditions (22 ms for choice MRT condition; 15 ms for simple MRT condition), but, when analyzing the MRT distributions, we did not find any clear evidence for express manual responses. The main difference in MRT distribution between simple and choice conditions was a shift towards shorter values for simple MRT.

Adult↗
PubMed1996

Interaction between facilitatory and inhibitory effects due to voluntary and automatic covert orienting of attention.

Covert orienting of attention to one spatial location improves the processing of signals occurring at this location at the expenses of the processing of signals occurring at other spatial positions. According to the premotor theory of visual attention, the voluntary orienting of attention to a peripheral position corresponds to the programming of a saccadic eye movement towards this position. A similar mechanism has been proposed to explain the inhibitory effects elicited by a non-informative peripheral cue. This review discusses some neural mechanisms involved in the facilitatory and inhibitory effects due to covert orienting of attention.

Attention↗
PubMed1994

ONSET and OFFSET inhibitions: effect of increase and decrease of cue luminance on manual reaction time to a visual target.

Simple reaction time (RT) to a peripheral visual target is shortened when a non-informative cue is flashed at the target location 100-150 ms before target onset (early facilitation). With longer intervals, RT to targets appearing at cue hemifield is lengthened (inhibition of return). In the present study, we investigated these effects inverting the stimulus contrast in relation to background to see how these effects are related to the onset and/or to the offset of a cue darker or brighter than background. Ten subjects were asked not to respond to a non-informative cue (S1) appearing on a computer screen 6 degrees to the right or to the left of the center of a fixation cross (FP), but to respond, by pressing a microswitch, to a target (S2) occurring at 4 degrees from the FP in the same hemifield as S1 or in the opposite hemifield. There were two different types of sessions. In one, S1 and S2 were bright against a dark background and in the other, S1 and S2 were dark against a bright background. In each session there were two types of trials. In OFF trials, each trial began with the presentation of FP. Five hundred ms later, S1 appeared and remained on for 700 ms. S2 appeared 100 or 800 ms after the offset of S1. In ON trials, S1 onset occurred 1200 ms after the beginning of the trial and remained on until the end of trial. S2 appeared 100 or 800 ms after S1 onset.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1994

Onset and offset of a visual cue have different effects on manual reaction time to a visual target.

Simple reaction time (RT) to a peripheral visual target is shortened when a non-informative cue is flashed at target location 100-150 ms before target onset (early facilitation). Afterwards, RT to targets appearing at cue location is lengthened (inhibition of return). In the present study we have investigated if these effects arise from the onset and/or from the offset of the cue and the time-dependence of these effects. Twelve subjects were asked not to respond to a non-informative cue (S1) appearing on a computer screen 6 degrees to the right or to the left of a fixation point (FP), but to respond, by pressing a key, to a target (S2) occurring at 4 degrees from the FP in the same hemifield as S1 or in the opposite hemifield. There were two different types of trials. In both, a brief auditory stimulus (W) occurring 700 ms after the onset of FP warned the subject that S2 would appear 100, 200, 300, 500 or 800 ms later. Trials where the onset of S1 coincides with W and S1 remains on until the response to S2 are called ON trials. In OFF trials, S1 onset occurs at the beginning of the trial and its offset coincides with W. We found that in ON trials, RTs to S2 occurring ipsi- or contralaterally to S1 did not differ. In contrast, S1 offset elicited an inhibition of its hemifield beginning at least 100 ms after S1 offset and extending up to 800 ms.

Acoustic Stimulation↗
PubMed1994

Spatial distribution of the inhibition elicited by the offset of a visual cue on manual reaction time to a visual target.

Simple reaction time (RT) to a peripheral visual target (S2) is shortened when a non-informative cue (S1) is flashed at the S2 location 100-150 ms before target onset (early facilitation). Afterwards, RTs to targets appearing at the S1 location are lengthened (inhibition of return). In the present investigation we studied the spatial distribution of the inhibition elicited by the offset of S1. Twelve subjects were asked not to respond to S1 which appeared on a horizontal meridian located 5.5 degrees above the fixation point (FP), but to respond, by pressing a key, to a target (S2) occurring at 5.5 degrees to the left or to the right. S1 could appear at one of 9 locations along this meridian (5.5, 3.5, 1.5, and 0.5 degrees to the left, 0.0 and 0.5, 1.5, 3.5, and 5.5 degrees to the right) and S2 occurred only at the most eccentric positions. Each trial began with the presentation of FP. Five-hundred ms later, S1 appeared and remained on for 700 ms. One hundred or 800 ms after S1 offset, S2 appeared in the same or in the opposite hemifield. We found that the offset of S1 elicits an inhibition (OFF-inhibition) which has the following features: a) it is maximal at cue's position; b) it spreads to other positions in the cued hemifield, and c) it decreases when the time interval between S1 offset and S2 onset increases from 100 to 800 ms.

Adult↗
PubMed1992

The retinal distribution of ganglion cells with crossed and uncrossed projections and the visual field representation in the opossum.

The retinal distribution of ganglion cells with crossed and uncrossed projections in the South American opossum, Didelphis marsupialis, was revealed by delivering HRP to one optic tract or to retinal targets of one hemisphere. The cells with uncrossed projections are restricted to the temporal retina, comprising 1/3 of the total retinal area, with a sharp transition at the naso-temporal boundary. Besides being distributed over the nasal 2/3 of the retina, cells with crossed projections are intermingled with those with uncrossed projections over the entire temporal retina. Quantitative analysis about the representation of the horizontal meridian on four specimens revealed that the maximum density of cells with uncrossed projections is on the average located at 3.2 mm (SD = 0.21), i.e. 34.8 deg, temporal to the optic disk, falling to 10% at 2.1 mm (SD = 0.14) or 22.8 deg. On the other hand, the peak for cells with crossed projections is more nasally placed at 1.8 mm (SD = 0.18), i.e. 19.6 deg. Between these two maxima, the site wherein the densities of cells with crossed and uncrossed projections are about equal is on the average about 2.7 mm (SD = 0.25) form the optic disk, i.e. 29.3 deg. This estimate supports the hypothesis that the retinal intersection of the vertical meridian lies within the region of split representation of crossed and uncrossed ganglion cells. In addition, it was observed that the opossum's retina has a large contingent of cells with uncrossed projections temporal to an eccentricity of 2.7 mm from the optic disk, where it represents roughly 2/3 of the ganglion cells. These data corroborate the relevance of the opossum as a non-primate model for visual work.

Animals↗
PubMed1988

The ipsilateral field representation in the striate cortex of the opossum.

Reference axes for the visuotopic study of the opossum's striate cortex were estimated from corresponding binocular response fields using multi-unit recording. These central binocular axes (CBA) were derived from experimental data based on the concept that corresponding receptive fields for each eye should be mostly in register under natural conditions. Vertical reference meridians, orthogonal to these axes, define a contralateral and an ipsilateral field for each eye with respect to the recording site. An ipsilateral field representation was observed for both eyes in the striate cortex at the transition zone with peristriate. Maximal values for the center and border of ipsilateral receptive fields were, respectively, 8 and 20 degrees for the contralateral eye and 6 and 14 degrees for the ipsilateral eye. An equivalent ipsilateral field representation was found in animals that had the anterior commissure cut prior to the recording session. This suggests that the ipsilateral field of both eyes may be represented in the striate cortex via the ipsilateral optic tract. Additionally, it was observed that the region of higher ganglion cell density in the retina shows a flattened distribution and that the CBA intersects the retina at the temporal aspect of this region.

Animals↗
PubMed1985

Visuotopic information conveyed by each eye to the opossum's superior colliculus.

The uniocular visual field representations on the superior colliculus (SC), as estimated from multiunit response field centres about the horizontal meridian, were compared in midpontine pretrigeminal opossums (Didelphis marsupialis aurita Wied 1826). Recordings from the rostral pole (RP) and its caudal neighbour, the direct binocular region (DBR), as defined by Rocha-Miranda et al. (1978), were distinguished by the histological control. The results showed that while the hemifield contralateral to the recording site was well represented on the DBR by both eyes, the ipsilateral hemifield was generously represented at the RP only by the contralateral eye. At the RP the ipsilateral eye usually conveyed information about the vertical meridian, bringing about an expanded representation of the central visual space. Distinct patterns of representation were also recognized on graphs which relate recording sites along the AP axis of the SC with the azimuths of response field centres. The representation of the vertical reference meridian upon this axis on an oculocentric system was estimated from the DBR data and localized in the RP, at about 500 microns from the rostral end, for the ipsilateral eye (Vo') and in the DBR, at about 800 microns for the other eye (Vo). Similarly, plots of the magnification factor against the AP collicular axis indicated different strategies of representation for each eye. At the segment between 500 and 800 microns on this axis the magnification factors of the ipsilateral eye were usually much higher than those of the other eye. Furthermore, horizontal disparities between field centres were shown to have distinct distributions along the AP axis within the RP and DBR regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Visuotopic organization of the superior colliculus of the opossum.

The representation of the visual field in the upper layers of the opossum's superior colliculus was studied by recording the response of multi-units to visual stimulation. Overall, the visual topography is similar to that of other non-primate mammals. Along the horizontal meridian and magnification factor decreases assymetrically about the vertical meridian, falling more abruptly in the region of the representation of the ipsilateral hemifield. The colliculus may be divided into three parts on the basis of the projections from the retina: a rostral region that does not receive any ipsilateral retinal afferents, a region that receives binocular retinal projections and a monocular region that receives only contralateral retinal input. Electrophysiological recording revealed that the rostral region contains a representation of 40 degrees of the ipsilateral field. The representation of the vertical meridian forms the border between the rostral region and the binocular region and the representation of the 40-45 degrees longitude meridian forms the border between the binocular and monocular regions.

Animals↗
PubMed1980

Electrocyte physiology: I. Temperature dependence of membrane excitability.

Some membrane characteristics of the isolated electrocyte of the Sachs organ are presented as function of temperature. Excitability curves are shown for electrocytes kept in standard saline at different temperatures. It is shown that rheobase varies directly with temperature. Apparently membrane resistance varies from 4.9 omega . cm2at 20 degrees C to 11.4 omega . cm2 at 5 degrees C and membrane capacity from 51,0 muF/cm2 to 48.4 muF/cm2 respectively. The relatively low resistance and high capacitance of this membrane may be due to an incorrect assessment of surface area owing to infolding.

Animals↗