Hans Colonius

Bimodal and trimodal multisensory enhancement: Effects of stimulus onset and intensity on reaction time

Manual reaction times to visual, auditory, and tactile stimuli presented simultaneously, or with a delay, were measured to test for multisensory interaction effects in a simple detection task with redundant signals. Responses to trimodal stimulus combinations were faster than those to bimodal combinations, which in turn were faster than reactions to unimodal stimuli. Response enhancement increased with decreasing auditory and tactile stimulus intensity and was a U-shaped function of stimulus onset asynchrony. Distribution inequality tests indicated that the multisensory interaction effects were larger than predicted by separate activation models, including the difference between bimodal and trimodal response facilitation. The results are discussed with respect to previous findings in a focused attention task and are compared with multisensory integration rules observed in bimodal and trimodal superior colliculus neurons in the cat and monkey.

Multisensory Interaction in Saccadic Reaction Time: A Time-Window-of-Integration Model

Saccadic reaction time to visual targets tends to be faster when stimuli from another modality (in particular, audition and touch) are presented in close temporal or spatial proximity even when subjects are instructed to ignore the accessory input (focused attention task). Multisensory interaction effects measured in neural structures involved in saccade generation (in particular, the superior colliculus) have demonstrated a similar spatio-temporal dependence. Neural network models of multisensory spatial integration have been shown to generate convergence of the visual, auditory, and tactile reference frames and the sensorimotor coordinate transformations necessary for coordinated head and eye movements. However, because these models do not capture the temporal coincidences critical for multisensory integration to occur, they cannot easily predict multisensory effects observed in behavioral data such as saccadic reaction times. This article proposes a quantitative stochastic framework, the time-window-of-integration model, to account for the temporal rules of multisensory integration. Saccadic responses collected from a visualtactile focused attention task are shown to be consistent with the time-window-of-integration model predictions.

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 ofsame anddifferent 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.

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.

Possibly dependent probability summation of reaction time

Abstract The redundant target effect is frequently observed in certain reaction time experiments. A probability summation mechanism is commonly invoked to explain the observed decrease of reaction time (RT). Here, probability summation models of RT are generalized by dropping the assumption of stochastic independence among processing times. An upper bound for the amount of statistical facilitation possible under negative dependence is derived for the bivariate case. Consequences for models of binocular summation and bisensory interaction are outlined and the main result is illustrated by a comparison of visual/auditory RT data with a simulated dependent probability summation mechanism. The impact of a base time component of reaction time in these simulations is characterized. Finally, it is shown that the detection paradigm can formally be treated under the reaction time paradigm.

Assessing age-related multisensory enhancement with the time-window-of-integration model

Although from multisensory research a great deal is known about how the different senses interact, there is little knowledge as to the impact of aging on these multisensory processes. In this study, we measured saccadic reaction time (SRT) of aged and young individuals to the onset of a visual target stimulus with and without an accessory auditory stimulus occurring (focused attention task). The response time pattern for both groups was similar: mean SRT to bimodal stimuli was generally shorter than to unimodal stimuli, and mean bimodal SRT was shorter when the auditory accessory was presented ipsilaterally rather than contralaterally to the target. The elderly participants were considerably slower than the younger participants under all conditions but showed a greater multisensory enhancement, that is, they seem to benefit more from bimodal stimulus presentation. In an attempt to weigh the contributions of peripheral sensory processes relative to more central cognitive processes possibly responsible for the difference in the younger and older adults, the time-window-of-integration (TWIN) model for crossmodal interaction in saccadic eye movements developed by the authors was fitted to the data from both groups. The model parameters suggest that (i) there is a slowing of the peripheral sensory processing in the elderly, (ii) as a result of this slowing, the probability of integration is smaller in the elderly even with a wider time-window-of-integration, and (iii) multisensory integration, if it occurs, manifests itself in larger neural enhancement in the elderly; however, because of (ii), on average the integration effect is not large enough to compensate for the peripheral slowing in the elderly.

The Race Model Inequality: Interpreting a Geometric Measure of the Amount of Violation

An inequality by J. O. Miller (1982) has become the standard tool to test the race model for redundant signals reaction times (RTs), as an alternative to a neural summation mechanism. It stipulates that the RT distribution function to redundant stimuli is never larger than the sum of the distribution functions for 2 single stimuli. When many different experimental conditions are to be compared, a numerical index of violation is very desirable. Widespread practice is to take a certain area with contours defined by the distribution functions for single and redundant stimuli. Here this area is shown to equal the difference between 2 mean RT values. This result provides an intuitive interpretation of the index and makes it amenable to simple statistical testing. An extension of this approach to 3 redundant signals is presented.

Intersensory facilitation in the motor component

SummaryIn the bimodal detection task the observer must respond as soon as a signal is presented in either of two modalities (e.g., a tone or a flash). A typical finding is a facilitation of reaction time for redundant signal trials, that is, when both signals are presented simultaneously or with a short delay. Models advanced for this effect imply either statistical facilitation (separate activation) or intersensory facilitation (coactivation). This paper reports a study investigating whether part of the facilitation can be accounted for by coactivation in the motor component. An analysis of the distributions of reaction time differences between left and right hand responses from a double response paradigm gave some evidence in favor of this hypothesis. In particular, our data suggest a u-shaped functional dependence of the amount of facilitation in the motor component on the interstimulus interval.

The “horse race” random utility model for choice probabilities and reaction times, and its competing risks interpretation

Random utility models have traditionally been applied to probabilistic choice data, with little attention to reaction times. We describe the class of “horse race” random utility models that can be applied to both choice probabilities and reaction times. We show that any (well behaved) set of choice probabilities and reaction times on a fixed set can be represented by an independent “horse race” random utility model, and relate this result to work in the theory of competing risks. We use the latter theory to motivate the condition that the option chosen and the time of choice be independent, a condition that is satisfied by a large class of (extreme value) “horse race” random utility models. Combining the latter condition with the assumption of an independent “horse race” random utility model yields a new characterization of Lute’s choice model, and a generalization of these conditions to subset choices (as opposed to choosing a single “best” element) yields the transition probabilities of Tversky’s elimination-by-aspects model.

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.