Visual Dominance Research Articles

Artificial crevice habitats to assess the biodiversity of vagile macro-cryptofauna of subtidal rocky reefs

Reef cryptofauna (animals inhabiting cracks and crevices) represent much of a reef’s biodiversity yet are seldom studied owing to their inaccessibility. Subtidal rocky reefs off Brunswick Heads and Byron Bay in northern New South Wales, Australia support benthic communities ranging from coral-dominated offshore reefs to kelp beds of Ecklonia radiata on inshore reefs. It was hypothesised that differential exposure to river discharge and the East Australian Current, as well as proximity to other reef habitats, may produce differences in recruitment and persistence of cryptofauna between superficially similar reefs within a small geographical range. Artificial crevice habitats were deployed at similar depths on three inshore reefs supporting similar Ecklonia densities. Although the species richness of crevice fauna was similar at all reefs, the species composition differed significantly along with the assemblages recruited in different seasons and to different crevice sizes. Neither reef faunas nor that of varying crevice sizes changed consistently with the seasons, yet all crevices appeared equally accessible to colonists. These results demonstrate the potential inadequacy of classifying reef communities for management of regional biodiversity based on the visual dominance of a few species that may not be as sensitive to environmental variables as many of the less obvious taxa.

Vibrotactile perception: examining the coding of vibrations and the just noticeable difference under various conditions

High-frequency vibrations are an essential part of numerous manipulation tasks. A promising research area, in particular, are telemanipulation tasks where vibrations occurring in the remote environment are fed back through tactile displays. Three experiments concerning the perception of vibrations were conducted. The first experiment aims at determining whether vibrations are coded primarily by frequency, amplitude, or acceleration by human participants. Results show that primarily frequency and amplitude, but not acceleration of the vibrations were perceived. In the second experiment, participants' just noticeable difference (JND) for frequency under different conditions was examined. The resulting JND of 18% for frequencies showed dependence neither on the amplitude or acceleration, which were independently held constant, nor on the reference frequencies. Therefore, it is not necessary to adjust the subjective intensity for vibrations for each human operator when designing and using tactile displays. In the third experiment, the stimuli and the procedure of the second experiment were replicated using different configurations and a mere force-output device. The resulting JNDs were 21% for vibrations of 100 Hz, and 17% for vibrations of 150 Hz and above. Furthermore, there was no visual dominance over the haptic modality regarding the JND for frequencies.

Audiovisual asynchrony modulates the Colavita visual dominance effect

Participants presented with unimodal auditory, unimodal visual, or bimodal audiovisual stimuli in a speeded discrimination task, fail to respond to the auditory component of bimodal targets significantly more often than they fail to respond to the visual component. We explored the influence of temporal factors on this phenomenon, known as the Colavita visual dominance effect. Participants performed a temporal order judgment (TOJ) task followed by the Colavita task. The stimulus onset asynchrony (SOA) between the auditory and visual components of the bimodal targets was varied and the results showed that the point at which the Colavita effect disappeared was correlated with the point at which participants started to reliably perceive the auditory stimulus as coming first. Furthermore, no Colavita effect was observed at those SOAs where the participants always perceived the visual stimulus as having come first. These results are explained in terms of the unity effect; that is, the Colavita visual dominance effect occurs within the temporal window in which participants bind auditory and visual stimuli into a single multisensory perceptual event. However, within this window, the Colavita effect is larger when the visual (rather than the auditory) stimulus is presented first.

Ergonomics recommendations for simultaneous and delayed presentation of visual and auditory signals

This study investigated the interaction effects of simultaneous and delayed presentations of visual and auditory signals on reaction times and response errors in a combined auditory-visual setting. The delay between visual and auditory (or auditory and visual) stimuli, and the intensity levels of the auditory signals were varied. In each trial the auditory and visual signals were presented either to the left or right of the subjects, who had to respond to the direction of signal that occurred earliest. It was found that visual stimuli tended to dominate auditory stimuli in the simultaneous presentation condition. However, this visual dominance effect was weakened with increasing intensity of the auditory signal. The visual dominance effect was also found when the two signals were presented with a small delay between them. Signal position, signal modality, signal presentation sequence and warning time were all found to affect performance. Some ergonomics recommendations based on these findings are given with the aim of improving the human–machine interface design in multi-sensory control consoles in order to enhance operator response speed and accuracy and overall system performance.

Semantic congruency and the Colavita visual dominance effect

Participants presented with auditory, visual, or bimodal audiovisual stimuli in a speeded discrimination task, fail to respond to the auditory component of bimodal targets significantly more often than to the visual component, a phenomenon known as the Colavita visual dominance effect. Given that spatial and temporal factors have recently been shown to modulate the Colavita effect, the aim of the present study, was to investigate whether semantic congruency also modulates the effect. In the three experiments reported here, participants were presented with a version of the Colavita task in which the stimulus congruency between the auditory and visual components of the bimodal targets was manipulated. That is, the auditory and visual stimuli could refer to the same or different object (in Experiments 1 and 2) or audiovisual speech event (Experiment 3). Surprisingly, semantic/stimulus congruency had no effect on the magnitude of the Colavita effect in any of the experiments, although it exerted a significant effect on certain other aspects of participants' performance. This finding contrasts with the results of other recent studies showing that semantic/stimulus congruency can affect certain multisensory interactions.

Visual dominance and attention: The Colavita effect revisited

Under many conditions, humans display a robust tendency to rely more on visual information than on other forms of sensory information. Colavita (1974) illustrated this visual dominance effect by showing that naive observers typically fail to respond to clearly suprathreshold tones if these are presented simultaneously with a visual target flash. In the present study, we demonstrate that visual dominance influences performance under more complex stimulation conditions and address the role played by attention in mediating this effect. In Experiment 1, we show the Colavita effect in the simple speeded detection of line drawings and naturalistic sounds, whereas in Experiment 2 we demonstrate visual dominance when the task targets (auditory, visual, or bimodal combinations) are embedded among continuous streams of irrelevant distractors. In Experiments 3-5, we address the consequences of varying the probability of occurrence of targets in each sensory modality. In Experiment 6, we further investigate the role played by attention on visual dominance by manipulating perceptual load in either the visual or the auditory modality. Our results demonstrate that selective attention to a particular sensory modality can modulate--although not completely reverse--visual dominance as illustrated by the Colavita effect.

Activity in the Posterior Parietal Cortex Mediates Visual Dominance over Kinesthesia

When both visual and kinesthetic information of a limb are available, vision is usually the dominant source of information used to perceive the spatial location. In this study, we conducted behavioral and functional magnetic resonance imaging (fMRI) experiments to examine the brain mechanisms underlying the visual dominance over kinesthesia in perceiving the position of a hand. We used tendon vibration to induce an illusory percept of flexion movement of an immobile hand, while the participants viewed a live image of either the vibrated or nonvibrated static hand through an on-line video camera. The intensity of illusory movement was significantly attenuated (for both the left and right hands) only when the participants viewed the static image of the vibrated hand. The fMRI study showed that the posterior parietal cortex (PPC) is specifically involved in the attenuation of illusory movement and that the activity of the PPC was associated with the degree of attenuation. This indicates that PPC is involved in the multisensory processing that occurs when vision overrules simultaneously available kinesthetic information for estimating the spatial location of a limb. It is thus suggested that the human parietal cortex may play a critical role in the maintenance of a coherent body image when the brain receives potentially conflicting multisensory information from the body.

Illusory colors promote interocular grouping during binocular rivalry

When dissimilar monocular images are presented separately to each of a person's eyes, these images compete for visual dominance, with dominance of one image or the other alternating over time. While this phenomenon, called binocular rivalry, transpires, local image features distributed over space and between the eyes can become visually dominant at the same time; the resulting global figure implicates interocular grouping. Previous studies have suggested that color tends to influence the incidence of global dominance; in this study, we assess whether illusory color can also influence interocular grouping. To test this, we exploited the McCollough effect, an orientation-contingent color aftereffect induced by prolonged adaptation to different colors paired with different orientations. Results show that during binocular rivalry, illusory colors induced by the McCollough adaptation enhance strong interocular grouping relative to preadaptation testing, to an extent comparable in strength with the enhancement induced by real colors. Thus, illusory colors that are present only in an observer's mind are sufficiently potent to influence low-level visual processes such as binocular rivalry.

Assessing the role of stimulus probability on the Colavita visual dominance effect

Participants presented with unimodal auditory (A), unimodal visual (V), or bimodal audiovisual stimuli (AV) in a task in which they have to identify the modality of the targets as rapidly as possible, fail to respond to the auditory component of bimodal targets significantly more often than they fail to respond to the visual component. In the majority of published studies on this phenomenon, known as the Colavita effect, the auditory, visual, and bimodal stimuli have been presented in the ratio 40A:40V:20AV. In the present study, we investigated whether the relatively low frequency with which the bimodal targets in previous studies have been presented may have contributed to participants’ difficulty in responding to such targets correctly. We manipulated the bimodal target probability by presenting the stimuli in the ratios 20A:20V:60AV, in Experiment 1; 5A:5V:90AV, 25A:25V:50AV, and 45A:45V:10AV, in Experiment 2. A significant Colavita visual dominance effect was observed when the bimodal targets were presented on 60% of the trials or less. We suggest that increasing the frequency of bimodal targets may have provided an exogenous cue to performance, that reduced the necessity for endogenous attention when selecting the appropriate response to make to bimodal targets.

Seeing the light: exploring the Colavita visual dominance effect

The Colavita visual dominance effect refers to the phenomenon whereby participants presented with unimodal auditory, unimodal visual, or bimodal audiovisual stimuli in a speeded discrimination task, fail to respond to the auditory component of bimodal targets significantly more often than they fail to respond to the visual component. The Colavita effect was demonstrated in this study when participants were presented with unimodal auditory, unimodal visual, or bimodal stimuli (in the ratios 40:40:20, Experiment 1; or 33:33:33, Experiment 2), to which they had to respond by pressing an auditory response key, a visual response key, or both response keys. The Colavita effect was also demonstrated when participants had to respond to the bimodal targets using a dedicated third (bimodal) response key (Experiment 3). These results therefore suggest that stimulus probability and the response demands of the task do not contribute significantly to the Colavita effect. In Experiment 4, we investigated what role exogenous attention toward a sensory modality plays in the Colavita effect. A significantly larger Colavita effect was observed when a visual cue preceded the bimodal target than when an auditory cue preceded it. This result suggests that the Colavita visual dominance effect can be partially explained in terms of the greater exogenous attention-capturing qualities of visual versus auditory stimuli.

Spatial coincidence modulates the Colavita visual dominance effect

The Colavita visual dominance effect refers to the phenomenon whereby participants presented with auditory, visual, or audiovisual stimuli in a speeded response task sometimes fail to respond to the auditory component of the bimodal targets. We conducted an experiment on the Colavita effect in which the auditory and visual components of the bimodal targets were presented from either the same or different positions (sides) at one of two eccentricities (13° or 26°). Participants were presented with auditory, visual, and bimodal stimuli to which they had to respond by pressing an auditory response key, a visual response key, or both response keys, respectively. On bimodal trials, participants failed to respond to the auditory stimulus significantly more often than they failed to respond to the visual stimulus, resulting in a significant Colavita visual dominance effect. The Colavita effect was significantly larger when the stimuli were presented from the same position than when they were presented from different positions. These results provide the first empirical evidence that the Colavita effect is modulated by the spatial coincidence of the auditory and visual stimuli.

Visual Dominance of Touch and the Somatosensory Homunculus: Does the Amount of Cortical Space Matter?

Visual Dominance of Touch and the Somatosensory Homunculus: Does the Amount of Cortical Space Matter?

The Influence of Spatial Delocation on Perceptual Integration of Vision and Touch

How do we perceive objects when what we see and what we touch is not at the same place? In a virtual environment, we observed that spatial delocation promotes visual dominance when judging the rotation angle of a hand-operated handle. Thus, the delocation of perceptual information appears to increase considerably the weight of the dominant sense at the expense of the other. We relate this result to the design of teleoperation and virtual reality systems, in which, typically, the visual and haptic sensory information originates in spatially distinct devices.

Synchronous and asynchronous presentations of auditory and visual signals: Implications for control console design

In this study, the effects of synchronous and asynchronous auditory and visual signal presentation on reaction times and response errors were examined to provide data for developing ergonomics recommendations for control console design. The results showed that synchronous presentation for combined visual and auditory stimulation facilitated responses, and shorter reaction times and higher response accuracies were obtained. When visual and auditory stimuli were presented synchronously but in opposing (left and right) positions, a visual dominance phenomenon was found, such that the subjects responded more often (81%) with faster responses to the visual signal. This visual dominance effect occurred even in the asynchronous condition when the auditory stimulus was presented 200 ms earlier than the visual one. It was also found that response speed and accuracy improved with increasing length of the warning time interval, and when an uncrossed hand posture was used for making responses. The above results were translated into practical ergonomic recommendations for response key layout, warning time interval, and ways of presenting visual and auditory signals to improve control console design.

The modality shift effect and the effectiveness of warning signals in different modalities

Which is better, a visual or an auditory warning signal? Initial findings suggested that an auditory signal was more effective, speeding reaction to a target more than a visual warning signal, particularly at brief foreperiods [Bertelson, P., & Tisseyre, F. (1969). The time-course of preparation: confirmatory results with visual and auditory warning signals. Acta Psychologica, 30. In W.G. Koster (Ed.), Attention and Performance II (pp. 145–154); Davis, R., & Green, F. A. (1969). Intersensory differences in the effect of warning signals on reaction time. Acta Psychologica, 30. In W.G. Koster (Ed.), Attention and Performance II (pp. 155–167)]. This led to the hypothesis that an auditory signal is more alerting than a visual warning signal [Sanders, A. F. (1975). The foreperiod effect revisited. Quarterly Journal of Experimental Psychology, 27, 591–598; Posner, M. I., Nissen, M. J., & Klein, R. M. (1976). Visual dominance: an information-processing account of its origins and significance. Psychological Review, 83, 157–171]. Recently [Turatto, M., Benso, F., Galfano, G., & Umilta, C. (2002). Nonspatial attentional shifts between audition and vision. Journal of Experimental Psychology: Human Perception and Performance, 28, 628–639] found no evidence for an auditory warning signal advantage and showed that at brief foreperiods a signal in the same modality as the target facilitated responding more than a signal in a different modality. They accounted for this result in terms of the modality shift effect, with the signal exogenously recruiting attention to its modality, and thereby facilitating responding to targets arriving in the modality to which attention had been recruited. The present study conducted six experiments to understand the cause of these conflicting findings. The results suggest that an auditory warning signal is not more effective than a visual warning signal. Previous reports of an auditory superiority appear to have been caused by using different locations for the visual warning signal and visual target, resulting in the target arriving at an unattended location when the foreperiod was brief. Turatto et al.’s results were replicated with a modality shift effect at brief foreperiods. However, it is also suggested that previous measures of the modality shift effect may still have been confounded by a location cuing effect.

The relationship between relative eye usage and ocular dominance shifts in cat visual cortex

A novel modification of the alternate monocular deprivation paradigm was used to quantitatively define the relationship between relative eye usage and the shift in visual cortical ocular dominance toward the advantaged eye. Both eyes of cats were alternately occluded by contact lenses during daily visual exposure sessions with varying ratios of relative eye usage: 1:1, 1.7:1, 3:1, 7:1, 50:1, 100:0. Only 100:0 and 50:1 ratios produced an ocular dominance shift in favor of the more experienced eye. The ocular dominance shift in 100:0 cats occurred in all cortical layers but only in extragranular layers of 50:1 cats. A steep power function described the data, indicating that an extreme imbalance in relative eye usage (>90%) is required for an ocular dominance shift.

Cochlear implants in children: safety as well as speech and language

The development of cochlear implants for children at the University of Melbourne and the Bionic Ear Institute, has consisted of a routine of biological and engineering safety followed by evaluation of speech processing strategies on adults before they are undertaken on children. The initial safety studies were to ensure that insertion was atraumatic, the electrical stimulus parameters did not lead to loss of ganglion cells and that the electrode could be inserted without the risk of middle ear infection leading to meningitis. The initial second formant extraction scheme was shown to produce significant open-set speech understanding in adults and was approved by the US Food and Drug Administration (FDA) in 1985. Following this, an international study was undertaken for the FDA on children using a strategy that also included the first formant, and was approved in 1990. Additional advances in speech processing have been evaluated on adults. However, before using one with high rates of stimulation, it was tested for safety on experimental animals. Further advances have been anticipated in particular through the development of a peri-modiolar array, the Nucleus Contour. Prior to its use on adults, it was tested in the human temporal bone and found to lead to minimal trauma. It was evaluated in adults and found to lead to better current localization and lower thresholds. A study was undertaken in children using a spectral maxima scheme at high rates (advanced combination encoder (ACE)) and the Contour array as it had given best results in adults. It was approved as safe and effective for use in children in 2000. Studies were also undertaken to look at plasticity and visual dominance particularly through cognitive studies and the use of the McGurk effect. This demonstrated that deaf children with implants rely heavily on visual information and there is a great need to have unambiguous auditory stimuli to get best results.

Cochlear implants in Children: safety as well as speech and language

The development of cochlear implants for children at the University of Melbourne/Bionic Ear Institute has consisted of a routine of biological and engineering safety followed by evaluation of speech processing strategies on adults before they are undertaken on children. The initial safety studies were to ensure that insertion was atraumatic, the electrical stimulus parameters did not lead to loss of ganglion cells and that the electrode could be inserted without the risk of middle ear infection leading to meningitis.The initial second formant extraction scheme was shown to produce significant open set speech understanding in adults and was approved by the U.S. Food and Drug Administration (FDA) in 1985. Following this, an international study was undertaken for the FDA on children using a strategy that also included the first formant, and was approved in 1990.Additional advances in speech processing have been evaluated on adults. However, before using one with high rates os stimulation it was tested for safety on experimental animals. Further advances have been anticipated in particular through the development of a perimodiolar array, the Nucleus “Contour.” Prior to its use on adults, it was tested in the human temporal bone and found to lead to minimal trauma. It was evaluated in adults and found to lead to better current localization and lower thresholds. A study was undertaken in children using a spectral maxima scheme at high rates (ACE) and the contour array as it had given best results in adults. It was approved as safe and effective for use in children in 2000.Studies have also been undertaken to look at plasticity and visual dominance particularly through cognitive studies and the use of the McGurk effect. This demonstrated that deaf children with implants rely heavily on visual information and there is a great need to have unambiguous auditory stimuli to get best results.

Auditory influences on visual temporal rate perception.

Visual stimuli are known to influence the perception of auditory stimuli in spatial tasks, giving rise to the ventriloquism effect. These influences can persist in the absence of visual input following a period of exposure to spatially disparate auditory and visual stimuli, a phenomenon termed the ventriloquism aftereffect. It has been speculated that the visual dominance over audition in spatial tasks is due to the superior spatial acuity of vision compared with audition. If that is the case, then the auditory system should dominate visual perception in a manner analogous to the ventriloquism effect and aftereffect if one uses a task in which the auditory system has superior acuity. To test this prediction, the interactions of visual and auditory stimuli were measured in a temporally based task in normal human subjects. The results show that the auditory system has a pronounced influence on visual temporal rate perception. This influence was independent of the spatial location, spectral bandwidth, and intensity of the auditory stimulus. The influence was, however, strongly dependent on the disparity in temporal rate between the two stimulus modalities. Further, aftereffects were observed following approximately 20 min of exposure to temporally disparate auditory and visual stimuli. These results show that the auditory system can strongly influence visual perception and are consistent with the idea that bimodal sensory conflicts are dominated by the sensory system with the greater acuity for the stimulus parameter being discriminated.

Humans integrate visual and haptic information in a statistically optimal fashion.

When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.