Biomedical subjects

Hans Colonius

Publications and source records attributed to Hans Colonius.

4 recordsLinked to original sources

PubMed2003

Two stages in crossmodal saccadic integration: evidence from a visual-auditory focused attention task.

Saccadic reaction time (SRT) toward a visual target stimulus was measured under simultaneous presentation of an auditory non-target (accessory stimulus). Horizontal position of the target was varied (25 degrees left and right of fixation) as well as position and intensity of the auditory accessory. SRT was reduced under the presence of the accessory, and it decreased both with increasing intensity of the auditory accessory and with decreasing distance between target and accessory. The absence of a significant interaction between distance and auditory intensity suggests (1) that the intensity of the accessory stimulus has no direct influence on the process of crossmodal integration, and (2) that spatial position and intensity of the accessory are processed in separate stages. This was supported by a probability inequality test showing that the amount of neural coactivation depends on spatial distance but not on auditory intensity. The results are discussed in the framework of a two-stage model assuming separate processing of unimodal and bimodal characteristics of the stimuli. These results are related to several recent neurophysiological findings.

Acoustic Stimulation↗

PubMed2003

Countermanding saccades: evidence against independent processing of go and stop signals.

In a stop signal paradigm, subjects were instructed to make a saccade to a visual target appearing left or right of the fixation point. In 25% of the trials, an auditory stop signal was presented after a variable delay that required the subject to inhibit the saccade. Observed saccadic response times in stop failure trials were longer than predicted by Logan and Cowan's (1984) race model. Saccadic response time and amplitude decreased with the time between stop signal presentation and saccade execution, suggesting an inhibitory effect between the stop signal and the go signal processes that is not compatible with an independent race assumption. Moreover, countermanding a saccade was more difficult when stop and go signals appeared at the same location.

Adult↗

PubMed2002

Visual-tactile spatial interaction in saccade generation.

Saccadic reaction times to visual targets tend to be faster when non-visual stimuli are presented in close temporal or spatial proximity even if subjects are instructed to ignore the accessory input. The effect tends to decrease with increasing spatial distance between the stimuli. Multisensory interaction effects measured in neural structures involved in saccade generation have demonstrated a similar spatial dependence. The present study investigated visual-tactile interaction effects on saccadic reaction time using a focused attention paradigm. Compared to unimodal visual targets saccadic reaction time to bimodal stimuli was reduced by up to 30 ms. The effect was larger for ipsi- than for contralateral presentations, and it increased with the eccentricity of the visual target. The results are consistent with attributing part of the facilitation to a multisensory effect of bimodal neurons with overlapping visual and tactile receptive field structures in the deep layers of the superior colliculus.

Adaptation, Physiological↗

PubMed2001

Multidimensional Fechnerian Scaling: Basics.

Fechnerian scaling is a theory of how a certain (Fechnerian) metric can be computed in a continuous stimulus space of arbitrary dimensionality from the shapes of psychometric (discrimination probability) functions taken in small vicinities of stimuli at which these functions reach their minima. This theory is rigorously derived in this paper from three assumptions about psychometric functions: (1) that they are continuous and have single minima around which they increase in all directions; (2) that any two stimulus differences from these minimum points that correspond to equal rises in discrimination probabilities are comeasurable in the small (i.e., asymptotically proportional), with a continuous coefficient of proportionality; and (3) that oppositely directed stimulus differences from a minimum point that correspond to equal rises in discrimination probabilities are equal in the small. A Fechnerian metric derived from these assumptions is an internal (or generalized Finsler) metric whose indicatrices are asymptotically similar to the horizontal cross-sections of the psychometric functions made just above their minima. Copyright 2001 Academic Press.

Journal Article↗