Synchrony of audio-visual speech stimuli modulates left superior temporal sulcus.

The superior temporal sulcus has been suggested to play a significant role in the integration of auditory and visual sensory information. Here, we presented vowels and short video clips of the corresponding articulatory gestures to healthy adult humans with two auditory-visual stimulus intervals during sparse sampling 3-T functional magnetic resonance imaging to detect which brain areas are sensitive to synchrony of speech sounds and associated articulatory gestures. The upper bank of the left middle superior temporal sulcus showed stronger activation during naturally asynchronous stimulation than during simultaneous stimulus presentation.

Perception of matching and conflicting audiovisual speech in dyslexic and fluent readers: an fMRI study at 3 T.

We presented phonetically matching and conflicting audiovisual vowels to 10 dyslexic and 10 fluent-reading young adults during "clustered volume acquisition" functional magnetic resonance imaging (fMRI) at 3 T. We further assessed co-variation between the dyslexic readers' phonological processing abilities, as indexed by neuropsychological test scores, and BOLD signal change within the visual cortex, auditory cortex, and Broca's area. Both dyslexic and fluent readers showed increased activation during observation of phonetically conflicting compared to matching vowels within the classical motor speech regions (Broca's area and the left premotor cortex), this activation difference being more extensive and bilateral in the dyslexic group.

Attention to visual speech gestures enhances hemodynamic activity in the left planum temporale.

Observing a speaker's articulatory gestures can contribute considerably to auditory speech perception. At the level of neural events, seen articulatory gestures can modify auditory cortex responses to speech sounds and modulate auditory cortex activity also in the absence of heard speech. However, possible effects of attention on this modulation have remained unclear.

Processing of audiovisual speech in Broca's area.

We investigated cerebral processing of audiovisual speech stimuli in humans using functional magnetic resonance imaging (fMRI). Ten healthy volunteers were scanned with a 'clustered volume acquisition' paradigm at 3 T during observation of phonetically matching (e.g.

Primary auditory cortex activation by visual speech: an fMRI study at 3 T.

Recent studies have yielded contradictory evidence on whether visual speech perception (watching articulatory gestures) can activate the human primary auditory cortex. To circumvent confounds due to inter-individual anatomical variation, we defined our subjects' Heschl's gyri and assessed blood oxygenation-dependent signal changes at 3 T within this confined region during visual speech perception and observation of moving circles. Visual speech perception activated Heschl's gyri in nine subjects, with activation in seven of them extending to the area of primary auditory cortex.

Adaptation of neuromagnetic N1 responses to phonetic stimuli by visual speech in humans.

The technique of 306-channel magnetoencephalogaphy (MEG) was used in eight healthy volunteers to test whether silent lip-reading modulates auditory-cortex processing of phonetic sounds. Auditory test stimuli (either Finnish vowel /ae/ or /ø/) were preceded by a 500 ms lag by either another auditory stimulus (/ae/, /ø/ or the second-formant midpoint between /ae/ and /ø/), or silent movie of a person articulating /ae/ or /ø/. Compared with N1 responses to auditory /ae/ and /ø/ when presented without a preceding stimulus, the amplitudes of left-hemisphere N1 responses to the test stimuli were significantly suppressed both when preceded by auditory and visual stimuli, this effect being significantly stronger with preceding auditory stimuli.

An electrophysiological correlate of human visual awareness.

In order to shed more light on the neural correlates of human visual awareness, event-related potentials (ERPs) were recorded in a perceptual threshold experiment. The masked stimuli (line-drawings of coherent, familiar objects and scrambled, meaningless non-objects) were presented below, near, and above the subjective perceptual threshold. A prominent negative ERP deflection, peaking around 260-270 ms from stimulus onset, was observed only for the stimuli reaching subjective visual awareness.

Visual awareness of low-contrast stimuli is reflected in event-related brain potentials.

Visual awareness was studied in 11 subjects by using coherent and scrambled objects as stimuli. The stimuli were presented near the subjective perceptual threshold. Explicitly recognized stimuli elicited a specific negative ERP deflection peaking at 460 ms.