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J E Albano

Publications and source records attributed to J E Albano.

10 recordsLinked to original sources
PubMed1996

Adaptive changes in saccade amplitude: oculocentric or orbitocentric mapping?

The saccadic system rapidly adjusts the amplitude of refixation movements to visual targets when abnormal postsaccadic errors occur. This is called rapid saccadic adaptation. It is not yet clear whether this form of adaptation produces changes related to oculocentric mechanisms, such as retinal error or motor error, or orbitocentric mechanisms, such as eye or gaze position. These experiments were designed to test whether rapid saccadic adaptation was orbitocentric, oculocentric, or both by creating a precise sensory motor mismatch between the visual target and the required saccade. Measurements were made to determine adaptive changes as function of (1) saccade direction; (2) eye position; and (3) saccade amplitude. Changes were found to be amplitude- and direction-specific but changes were generalized across a broad range of orbital positions. Two conditions of adaptation: increasing and decreasing amplitude, produced quantitatively similar results, indicating that similar mechanisms underlie both processes. Thus, these data support the view that changes during rapid saccadic adaptation are organized principally in a retina-referenced (oculocentric) map, but only broadly, if at all, in a head-referenced (orbitocentric) map. The changes are consistent with a mechanism represented in a spatial mapping of either retinal or motor error.

Adaptation, Ocular↗
PubMed1995

Binocular interactions in rapid saccadic adaptation.

An adaptive mechanism controls the strength of innervation to the two eyes independently. However, under some circumstances an adjustment in strength of innervation to one eye is generalized to the other. The coupling and uncoupling of the two eyes during saccadic motor learning was studied using the technique of intrasaccadic target displacements to provide a precise visual-motor error proportional to the commanded movement. Early adaptive changes (saccade plus fast vergence) were measured within the saccadic interval and late adaptive changes (vergence error) were measured after the saccadic interval. When one viewing eye was retrained using intrasaccadic displacements, saccadic amplitude changes generalized to the other nonviewing eye. Thus, rapid adaptive changes trained monocularly were transferred to the nonviewing eye. But when two eyes were viewing and an adaptive stimulus was provided to only one eye (binocular viewing-monocular training), adaptive changes also occurred in both eyes. Experiments described here suggest that the recalibration of the saccade occurs quickly as a conjugate adjustment of gain which is used to balance innervation to the two eyes. Thereafter, disconjugate mechanisms provide a further recalibration to each eye independently.

Adaptation, Physiological↗
PubMed1990

The role of directionally selective neurons in the perception of global motion.

Dynamic random dot targets consisting of many localized motion vectors have been used to study the pooling of local motion signals into a global motion percept (Williams and Sekuler, 1984). In such displays, the dots are displaced with a constant step size and the direction of motion for each dot is chosen at random from a specified distribution. When the distribution extends over 360 deg, the display consists only of local random motion of individual dots and no coherent motion is reported. However, when the distribution is less than 360 deg (biased), the stimulus appears to flow in a single direction. We examined the effects of reducing the number of directionally selective (DS) cortical neurons on this integration process. Normal cats and cats with severely reduced proportions of DS neurons were trained on 2 direction discrimination tasks. The discrimination of opposite directions was examined while varying either the range of directions of local motion, or the proportion of dots moving with biased distribution. When all dots in the display were directionally biased, cats with reduced numbers of DS neurons performed the task as well as normal cats and humans (threshold range: 280-320 deg). However, when the proportion of biased dots decreased, these animals had severe deficits. Thus, in the absence of noise, even a very small number of DS neurons can perform spatial pooling of local directional signals, and support normal discrimination of opposite directions. However, a full complement of directional detectors appears necessary when the motion signal is masked by noise. The discrimination of small differences in direction revealed far more severe deficits, even when all the dots in the display were directionally biased (no noise).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Rapid adaptation of saccadic amplitude in humans and monkeys.

To study adaptive motor learning in the saccadic system we have used a psychophysical procedure that introduces a "visuomotor mismatch" between the retinal error signal (retinal distance between fovea and target image) and the motor error signal (movement required to accurately foveate the target). The saccadic system responds to this visuomotor mismatch by rapidly modifying the amplitude of the saccade. We will refer to this procedure as induced saccadic dysmetria. In our paradigm, the saccadic dysmetria is produced by electronically adding or subtracting a fraction of the eye position signal to adjust the target's position. Thus the original visual error signal that initiates the saccade no longer elicits an appropriately sized saccade; there is a mismatch between target step and saccade amplitude. We find that the human and nonhuman primate saccadic systems respond to this error by rapidly and adaptively adjusting the amplitude of saccades. Such adaptive adjustments are not the result of changes in saccade strategy but represent a genuine recalibration. We conclude that induced saccadic dysmetria provides us with a tool for the study of adaptive motor learning in the oculomotor system. It is hypothesized that the adaptive mechanism may use either or both of two signals: a visual error signal representing the retinal distance of the target from the fovea after the initial saccade and/or a motor error signal represented by the amplitude of the corrective saccade.

Adaptation, Ocular↗
PubMed1979

Laminar origin of projections from the superficial layers of the superior colliculus in the tree shrew, Tupaia glis.

The laminar origin of the efferent projections from the superior colliculus to the pulvinar and to the dorsal and ventral lateral geniculate nuclei has been studied using the retrograde axonal transport of horseradish peroxidase. Following injections in either the dorsal or the ventral lateral geniculate nucleus, cells heavily labeled with the horseradish peroxidase reaction product are restricted primarily to the upper stratum griseum superficiale. These cells have small, fusiform somas with dendrites which extend dorsally and ventrally, perpendicular to the pial surface. In contrast, following injections in the pulvinar, cells labeled with reaction product are restricted primarily to the lower stratum griseum superficiale and to the most superficial part of stratum opticum. These cells typically have larger somas than cells in the upper stratum griseum superficiale, and often have dendrites which emerge horizontally from the cell body. When taken together with previous electrophysiological and anatomical studies, the present findings suggest that there is a laminar subdivision of the tree shrew stratum griseum superficiale, and that these subdivisions project selectively to different thalamic targets.

Animals↗