A bias-free two-alternative forced choice procedure to examine intersensory illusions applied to the ventriloquist effect by flashes and averted eye-gazes (original) (raw)
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Illusory sound shifts induced by the ventriloquist illusion evoke the mismatch negativity
Neuroscience Letters, 2004
The ventriloquist illusion arises when sounds are mislocated towards a synchronous but spatially discrepant visual event. Here, we investigated the ventriloquist illusion at a neurophysiological level. The question was whether an illusory shift in sound location was reflected in the auditory mismatch negativity (MMN). An 'oddball' paradigm was used whereby simultaneously presented sounds and flashes coming from the same location served as standard. The deviant consisted of a sound originating from the same source as the standard together with a flash at 208 spatial separation, which evoked an illusory sound shift. This illusory sound shift evoked an MMN closely resembling the MMN evoked by an actual sound shift. A visual-only control condition ruled out that the illusory-evoked MMN was confounded by the visual part of the audiovisual deviant. These results indicate that the crossmodal interaction on which the ventriloquist illusion is based takes place automatically at an early processing stage, within 200 ms after stimulus onset. q
The ventriloquist effect does not depend on the direction of deliberatevisual attention
2000
It is well known that discrepancies in the location of synchronized auditory and visual events can lead to mislocalizations of the auditory source, so-called ventriloquism. In two experiments, we tested whether such cross-modal influences on auditory localization depend on deliberate visual attention to the biasing visual event. In Experiment 1, subjects pointed to the apparent source of sounds in the presence or absence of a synchronous peripheral flash. They also monitored for target visual events, either at the location of the peripheral flash or in a central location. Auditory localization was attracted toward the synchronous peripheral flash, but this was unaffected by where deliberate visual attention was directed in the monitoring task. In Experiment 2, bilateral flashes were presented in synchrony with each sound, to provide competing visual attractors. When these visual events were equally salient on the two sides, auditory localization was unaffected by which side subjects monitored for visual targets. When one flash was larger than the other, auditory localization was slightly but reliably attracted toward it, but again regardless of where visual monitoring was required. We conclude that ventriloquism largely reflects automatic sensory interactions, with little or no role for deliberate spatial attention.
The ventriloquist effect does not depend on the direction of automatic visual attention
Attention Perception & Psychophysics, 2001
Previously, we showed that the visual bias of auditory sound location, or ventriloquism, does not depend on the direction of deliberate, orendogenous, attention (Bertelson, Vroomen, de Gelder, & Driver, 2000). In the present study, a similar question concerning automatic, orexogenous, attention was examined. The experimental manipulation was based on the fact that exogenous visual attention can be attracted toward asingleton—that is, an item different on some dimension from all other items presented simultaneously. A display was used that consisted of a row of four bright squares with one square, in either the left- or the rightmost position,smaller than the others, serving as the singleton. In Experiment 1, subjects made dichotomous left-right judgments concerning sound bursts, whose successivelocations were controlled by a psychophysical staircase procedure and which were presented in synchrony with a display with the singleton either left or right. Results showed that the apparent location of the sound was attractednot toward the singleton, but instead toward the big squares at the opposite end of the display. Experiment 2 was run to check that the singleton effectively attracted exogenous attention. The task was to discriminate target letters presented either on the singleton or on the opposite big square. Performance deteriorated when the target was on the big square opposite the singleton, in comparison with control trials with no singleton, thus showing that the singleton attracted attention away from the target location. In Experiment 3, localization and discrimination trials were mixed randomly so as to control for potential differences in subjects’ strategies in the two preceding experiments. Results were as before, showing that the singleton attracted attention, whereas sound localization was shifted away from the singleton. Ventriloquism can thus be dissociated from exogenous visual attention and appears to reflect sensory interactions with little role for the direction of visual spatial attention.
Directing spatial attention towards the illusory location of a ventriloquized sound
Acta Psychologica, 2001
In this study, we examined whether ventriloquism can rearrange external space on which spatial re¯exive attention operates. The task was to judge the elevation (up vs down) of auditory targets delivered in the left or the right periphery, taking no account of side of presentation. Targets were preceded by either auditory, visual, or audiovisual cues to that side. Auditory, but not visual cues had an eect on the speed of auditory target discrimination. On the other hand, a ventriloquized cue, consisting of a tone in central location synchronized with a light¯ash in the periphery, facilitated responses to targets appearing on the same side as thē ash. That eect presumably resulted from the attraction of the apparent location of the tone towards the¯ash, a well-known manifestation of ventriloquism. Ventriloquism thus can reorganize space in which re¯exive attention operates. Ó
Clinical Neurophysiology, 2002
The ventriloquism effect is the tendency to underestimate the spatial separation between synchronous auditory and visual signals moderately separated in space. If, as it is thought, this effect is pre-attentive, it could modulate the mismatch negativity (MMN) that indexes the automatic, pre-attentive detection of deviant auditory stimuli rarely occurring in a sequence of standard stimuli. We assessed the existence of an MMN evoked by auditory and visual signals made up of standard sounds coming from the same location as the visual signal and deviant sounds coming from lateral deviations (20 or 608). As first observed in a behavioral study, a ventriloquism effect occurred for 208 spatial separation but not for 608.
The ventriloquism illusion does modulate the Mismatch Negativity (MMN)
Audiovisual interactions observed in the ventriloquism and McGurk illusions were compared, using the same materials. The ventriloquism effect was estimated through a discordance detection task and the McGurk illusion through an identification task. The stimuli were visually displayed on a screen located in front of the participants' head and acoustically delivered through one of nine hidden loudspeakers located from straight ahead (0°) to 80° (20° steps) left and right. The speaker's face was either upright or inverted. The ventriloquism effect was affected by the degree of spatial separation, but unaffected by upright vs. inverted presentation of the face, or by the congruency of the stimuli. The McGurk illusion was of the same size whatever the loudspeaker location but was reduced by face inversion. The differences in the spatial and cognitive rules that govern both interactions are discussed in terms of specific functionality of the underlying mechanisms.