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H Colonius

Publications and source records attributed to H Colonius.

10 recordsLinked to original sources
PubMed2001

Countermanding saccades with auditory stop signals: testing the race model.

In a stop signal paradigm to investigate the control of human saccades subjects were instructed to make a saccade to a visual target appearing suddenly l5 degrees to the left or to the 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. The stop signal was presented randomly at the target position, at the opposite side, or at fixation. Using different estimation techniques the average time needed to inhibit a saccade (stop signal processing time, or SSPT) was estimated on the basis of the race model. The SSPT estimates ranging from 50 to 100 ms (depending on subject) are shorter than those from previous studies with visual stop signals. Position of the auditory stop signal did not show an effect on countermanding effectiveness. We found saccadic response times consistent with the race model predictions for two subjects, while a third subject showed small but consistent violations. Moreover, all subjects showed a tendency towards hypometric saccades for responses that could not be inhibited. These findings are discussed with respect to recent neurophysiological results.

Acoustic Stimulation↗
PubMed2001

A two-stage model for visual-auditory interaction in saccadic latencies.

In two experiments, saccadic response time (SRT) for eye movements toward visual target stimuli at different horizontal positions was measured under simultaneous or near-simultaneous presentation of an auditory nontarget (distractor). The horizontal position of the auditory signal was varied, using a virtual auditory environment setup. Mean SRT to a visual target increased with distance to the auditory nontarget and with delay of the onset of the auditory signal relative to the onset of the visual stimulus. A stochastic model is presented that distinguishes a peripheral processing stage with separate parallel activation by visual and auditory information from a central processing stage at which intersensory integration takes place. Two model versions differing with respect to the role of the auditory distractors are tested against the SRT data.

Adult↗
PubMed2000

A comparison of two response time models applied to perceptual matching.

Two models, a Poisson race model and a diffusion model, are fit to data from a perceptual matching task. In each model, information about the similarity or the difference between two stimuli accumulates toward thresholds for either response. Stimulus variables are assumed to influence the rate at which information accumulates, and response variables are assumed to influence the level of the response thresholds. Three experiments were conducted to assess the performance of each model. In Experiment 1, observers performed under different response deadlines; in Experiment 2, response bias was manipulated by changing the relative frequency of same and different stimuli. In Experiment 3, stimulus pairs were presented at three eccentricities: foveal, parafoveal, and peripheral. We examined whether the race and diffusion models could fit the response time and accuracy data through changes only in response parameters (for Experiments 1 and 2) or stimulus parameters (for Experiment 3). Comparisons between the two models suggest that the race model, which has not been studied extensively, can account for perceptual matching data at least as well as the diffusion model. Furthermore, without the constraints on the parameters provided by the experimental conditions, the diffusion and the race models are indistinguishable. This finding emphasizes the importance of fitting models across several conditions and imposing logical psychological constraints on the parameters of models.

Adult↗
PubMed1999

Fechnerian metrics in unidimensional and multidimensional stimulus spaces.

A new theory is proposed for subjective (Fechnerian) distances among stimuli in a continuous stimulus space of arbitrary dimensionality. Each stimulus in such a space is associated with a psychometric function that determines probabilities with which it is discriminated from other stimuli, and a certain measure of its discriminability from its infinitesimally close neighboring stimuli is computed from the shape of this psychometric function in the vicinity of its minimum. This measure of discriminability can be integrated along any path connecting any two points in the stimulus space, yielding the psychometric length of this path. The Fechnerian distance between two stimuli is defined as the infimum of the psychometric lengths of all paths connecting the two stimuli. For a broad class of models defining the dichotomy of response bias versus discriminability, the Fechnerian distances are invariant under response bias changes. In the case in which physically multidimensional stimuli are discriminated along some unidimensional subjective attribute, a systematic construction of the Fechnerian metric leads to a resolution of the long-standing controversy related to the numbers of just-noticeable differences between isosensitivity curves. It is argued that for unidimensional stimulus continua, the proposed theory is close to the intended meaning of Fechner's original theory.

Discrimination, Psychological↗
PubMed1997

Parallel Processing Response Times and Experimental Determination of the Stopping Rule

It was formerly demonstrated that virtually all reasonable exhaustive serial models, and a more constrained set of exhaustive parallel models, cannot predict critical effects associated with self-terminating models. The present investigation greatly generalizes the parallel class of models covered by similar "impossibility" theorems. Specifically, we prove that if an exhaustive parallel model is not super capacity, and if targets are processed at least as fast as non-targets, then it cannot predict such (self-terminating) effects. Such effects are ubiquitous in the experimental literature, offering strong confirmation for self-terminating processing. Copyright 1997 Academic Press. Copyright 1997 Academic Press

Journal Article↗
PubMed1997

Auditory profile analysis: is there perceptual constancy for spectral shape for stimuli roved in frequency?

The ability to discriminate between two spectral shapes was investigated using a one-interval, two-alternative forced choice procedure. Each stimulus consisted of seven components equally spaced on a logarithmic frequency scale (frequency ratio of 1.2 between adjacent components). The two spectral shapes were produced by first generating a complex each of whose components was equally loud (when heard in isolation) and then increasing the level of either the third or the fifth component by a certain amount. To render pitch an unusable cue, the center frequencies of the stimuli were randomly varied between presentations (maintaining the ratio between adjacent components) over a range of about three octaves (279-2074 Hz). The data indicate that listeners were not able to distinguish between the two types of profiles even for very large increments in level of the third and the fifth components. The results suggest that there is no perceptual constancy for this type of spectral shape for stimuli roved over a sufficiently large frequency range. The spectral shape cannot be perceived independently of stimulus frequency. The results are related to the multi-channel model applied in profile analysis tasks.

Adult↗