Tobias S Andersen | PubMed Health

PubMed2005

Maximum Likelihood Integration of rapid flashes and beeps.

Maximum likelihood models of multisensory integration are theoretically attractive because the goals and assumptions of sensory information processing are explicitly stated in such optimal models. When subjects perceive stimuli categorically, as opposed to on a continuous scale, Maximum Likelihood Integration (MLI) can occur before or after categorization-early or late. We introduce early MLI and apply it to the audiovisual perception of rapid beeps and flashes. We compare it to late MLI and show that early MLI is a better fitting and more parsimonious model. We also show that early MLI is better able to account for the effects of information reliability, modality appropriateness and intermodal attention which affect multisensory perception.

Acoustic Stimulation↗

PubMed2004

Audio-visual speech perception is special.

In face-to-face conversation speech is perceived by ear and eye. We studied the prerequisites of audio-visual speech perception by using perceptually ambiguous sine wave replicas of natural speech as auditory stimuli. When the subjects were not aware that the auditory stimuli were speech, they showed only negligible integration of auditory and visual stimuli. When the same subjects learned to perceive the same auditory stimuli as speech, they integrated the auditory and visual stimuli in a similar manner as natural speech. These results demonstrate the existence of a multisensory speech-specific mode of perception.

Association Learning↗

PubMed2004

Factors influencing audiovisual fission and fusion illusions.

Information processing in auditory and visual modalities interacts in many circumstances. Spatially and temporally coincident acoustic and visual information are often bound together to form multisensory percepts [B.E. Stein, M.A. Meredith, The Merging of the Senses, A Bradford Book, Cambridge, MA, (1993), 211 pp.; Psychol. Bull. 88 (1980) 638]. Shams et al. recently reported a multisensory fission illusion where a single flash is perceived as two flashes when two rapid tone beeps are presented concurrently [Nature 408 (2000) 788; Cogn. Brain Res. 14 (2002) 147]. The absence of a fusion illusion, where two flashes would fuse to one when accompanied by one beep, indicated a perceptual rather than cognitive nature of the illusion. Here we report both fusion and fission illusions using stimuli very similar to those used by Shams et al. By instructing subjects to count beeps rather than flashes and decreasing the sound intensity to near threshold, we also created a corresponding visually induced auditory illusion. We discuss our results in light of four hypotheses of multisensory integration, each advocating a condition for modality dominance. According to the discontinuity hypothesis [Cogn. Brain Res. 14 (2002) 147], the modality in which stimulation is discontinuous dominates. The modality appropriateness hypothesis [Psychol. Bull. 88 (1980) 638] states that the modality more appropriate for the task at hand dominates. The information reliability hypothesis [J.-L. Schwartz, J. Robert-Ribes, P. Escudier, Ten years after Summerfield: a taxonomy of models for audio-visual fusion in speech perception. In: R. Campbell (Ed.), Hearing by Eye: The Psychology of Lipreading, Lawrence Earlbaum Associates, Hove, UK, (1998), pp. 3-51] claims that the modality providing more reliable information dominates. In strong forms, none of these three hypotheses applies to our data. We re-state the hypotheses in weak forms so that discontinuity, modality appropriateness and information reliability are factors which increase a modality's tendency to dominate. All these factors are important in explaining our data. Finally, we interpret the effect of instructions in light of the directed attention hypothesis which states that the attended modality is dominant [Psychol. Bull. 88 (1980) 638].

Acoustic Stimulation↗