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Multisensory integration + Motor control

Sunday, October 02nd,   2011 [18:00 - 20:00]

PS_3.031 - When a non specific action enhances visual entry

Vallet, G. 1, 2, 3 & Shore, D. 1

1 Multisensory Perception Laboratory (PNB), McMaster University; Hamilton, Canada
2 Laboratoire EMC, Lyon2 University, Lyon, France
3 School of Psychology, Laval University, Quebec City, Canada

Objective. Explore how action can influence the perception and integration of multisensory stimuli.
Method. Participants initiated each trial by pressing a left or a right key of the keyboard. A visual or an auditory stimulus was presented immediately (0ms SOA) or after 500ms. The second stimulus was presented after an additional 100, 200, 300 or 400ms. The light (Experiment 1) or the sound (Experiment 2) was lateralized to the ipsilateral or contralateral side of the action. Observers judged which of the two stimuli were presented first. Results. The point of subjective simultaneity (PSS) and just noticeable difference (JND) was computed. The PSS was shifted between the two SOAs such that the auditory stimulus had to be presented sooner in the 0 SOA condition (-106ms) compared to the 500ms SOA condition (-14ms). This contrasts starkly with classical results where the light must be presented before the sound (50ms) to be perceived simultaneously. The JND was smaller for the 0ms SOA condition. There was no effect of side of presentation. Conclusion. Action seems to speed the processing of visual stimuli relative to auditory stimuli. There was no support for the application of the unity assumption with action.

PS_3.032 - Establishing and relearning action-effect associations

Nattkemper, D. & Frensch, P. A.

Humboldt University Berlin, Germany

Investigating the effects of action-effect compatibility has provided valuable insights into human action control. These studies show that responses are initiated faster if there is an overlap between features of the response and features of the effect. This observation emerged (among others) from experiments showing that a variant of the so-called SNARC-effect can be generated when persons produce numbers by key-presses. The SNARC-effect is a spatial compatibility effect which is usually observed when numbers are processed. Small numbers are preferentially responded to with the left hand and large numbers with the right hand. For explanation it is assumed that mental representations of numbers are associated with spatial information; relatively small numbers are associated with ?left? and relatively large numbers with ?right?. These relative spatial codes get activated when number identity is processed. Similar effects are observed when persons produce nominally task-irrelevant numbers by key-press responses to visual stimuli: Small numbers are preferentially produced with the left hand and large numbers with the right hand. This suggests that participants represented the relations between actions and their effects and used this knowledge in action control. We report a series of studies that aimed at investigating the details of action-effect acquisition and usage.

PS_3.033 - Effects of visual speech on syllable processing speed in babble and white noise: An event-related potential study

Valsø, A. M. & Behne, D. M.

Speech Lab, Psychology Department, Norwegian University of Science and Technology

Behavioral research on audio-visual speech perception has long shown an increased use of visual information when speech is imbedded in white noise (e.g., Sumby & Pollack, 1954). More recently, use of visual speech information has been shown to be even greater in babble than white noise (e.g. Alm et al., 2009). The current study investigates temporal effects of white noise and cafeteria babble on speech processing, and the effect of visual speech on the respective conditions. Continuous EEG was recorded while thirteen healthy Norwegians were presented with audio-visual, audio-only, and visual-only productions of the syllable /ba/ in quiet or masked with white noise or babble. Latency analyses of the N1 component showed that early speech processing was later in noise conditions compared to quiet, and to a greater degree in cafeteria babble than in white noise. Results also showed that the access to visual speech cues increased processing speed in the noisy conditions and reduced the gap in processing speed of syllables between quiet and noise. These findings will be discussed in terms of the principle of inverse effectiveness

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