Renaud Brochard

Perceiving rhythm where none exists: Event-Related Potential (ERP) correlates of subjective accenting

Previous research suggests that our past experience of rhythmic structure in music results in a tendency for Western listeners to subjectively accent equitonal isochronous sequences. We have shown in an earlier study that the occurrence of a slightly softer tone in the 8th to 11th position of such a sequence evokes a P300 event-related potential (ERP) response of different amplitudes depending on whether the tone occurs in putatively subjectively accented or unaccented sequence positions (Brochard et al., 2003). One current theory of rhythm processing postulates that subjective accenting is the result of predictive modulations of perceptual processes by the attention system. If this is the case then ERP modulations should be observed at an earlier latency than the P300 and these should be observed in ERPs to both standard and softer tones. Such effects were not observed in our previous study. This was possibly due to the use of a linked-mastoid reference which may have obscured lateralized differences. The aim of the present study was to replicate the previous auditory P300 subjective accenting findings and to investigate the possibility that these effects are preceded by ERP changes that are indicative of rhythmic modulation of perceptual processing. Previous auditory P300 findings were replicated. In addition and consistent with current theories of rhythm processing, early brain ERP differences were observed both in standard and deviant tones from the onset of the stimulus. These left lateralized differences are consistent with a rhythmic, endogenously driven, modulation of perception that influences the conscious experience of equitonal isochronous sequences.

Got rhythm…for better and for worse. Cross-modal effects of auditory rhythm on visual word recognition.

The present research aimed to investigate whether, as previously observed with pictures, background auditory rhythm would also influence visual word recognition. In a lexical decision task, participants were presented with bisyllabic visual words, segmented into two successive groups of letters, while an irrelevant strongly metric auditory sequence was played in a loop. The first group of letters could either be congruent with the syllabic division of the word (e.g. val in val/se) or not (e.g. va in va/lse). In agreement with the Dynamic Attending Theory (DAT), our results confirmed that the presentation of the correct first syllable on-beat (i.e. in synchrony with a peak of covert attention) facilitated visual word recognition compared to when it was presented off-beat. However, when an incongruent first syllable was displayed on-beat, this led to an aggravation of impaired recognition. Thus, our results suggest that oscillatory attention tapped into cognitive processes rather than perceptual or decisional and motor stages. We like to think of our paradigm, which combines background auditory rhythm with segmented visual stimuli, as a sort of temporal magnifying glass which allows for the enlargement of the reaction time differences between beneficial and detrimental processing conditions in human cognition.

Visual motion disambiguation by a subliminal sound

There is growing interest in the effect of sound on visual motion perception. One model involves the illusion created when two identical objects moving towards each other on a two-dimensional visual display can be seen to either bounce off or stream through each other. Previous studies show that the large bias normally seen toward the streaming percept can be modulated by the presentation of an auditory event at the moment of coincidence. However, no reports to date provide sufficient evidence to indicate whether the sound bounce-inducing effect is due to a perceptual binding process or merely to an explicit inference resulting from the transient auditory stimulus resembling a physical collision of two objects. In the present study, we used a novel experimental design in which a subliminal sound was presented either 150 ms before, at, or 150 ms after the moment of coincidence of two disks moving towards each other. The results showed that there was an increased perception of bouncing (rather than streaming) when the subliminal sound was presented at or 150 ms after the moment of coincidence compared to when no sound was presented. These findings provide the first empirical demonstration that activation of the human auditory system without reaching consciousness affects the perception of an ambiguous visual motion display.

Evidence of beat perception via purely tactile stimulation

Humans can easily tap in synchrony with an auditory beat but not with an equivalent visual rhythmic sequence, suggesting that the sensation of meter (i.e. of an underlying regular pulse) may be inherently auditory. We assessed whether the perception of meter could also be felt with tactile sensory inputs. We found that, when participants were presented with identical rhythmic sequences filled with either short tones or hand stimulations, they could more efficiently tap in synchrony with strongly rather than weakly metric sequences. These observations suggest that non-musician adults can extract the metric structure of purely tactile rhythms and use it to tap regularly with the beat induced by such sequences. This finding represents a challenge for present models of rhythm processing.

Brain Lateralization of Metrical Accenting in Musicians

The perception of meter, or the alternation of strong and weak beats, was assessed in musically trained listeners through magnetoencephalography. Metrical accents were examined with no temporal disruption of the serial grouping of tones. Results showed an effect of metrical processing among identical standard tones in the left hemisphere, with larger responses on strong than on weak beats. Moreover, processing of occasional increases in intensity (phenomenal accents) varied as a function of metrical position in the left hemisphere, but not in the right. Our findings support the view of a relatively early, left‐hemispheric effect of metrical processing in musicians.

Auditory temporal processing in schizophrenia: High level rather than low level deficits?

Introduction: Patients with schizophrenia demonstrate a wide range of information processing deficits. Most recent studies argue in favour of high level deficits, including attention and context processing, whereas fewer studies have demonstrated deficits at earlier stages of processing, such as perceptual discrimination and organisation. This is the first study to investigate both high and low level processing, within a single paradigm, in the case of auditory temporal processing in schizophrenia. Methods: Patients with schizophrenia were compared to controls on a series of tasks involving three auditory temporal processes varying from low to higher level: (1) segregation of a complex sequence into component auditory streams; (2) detection of local temporal irregularities within a stream; (3) attentional focusing on one stream by the use of a cue preceding the complex sequence. Results: The lowest level of processing examined here--stream segregation--appeared to function equally well in patients as in controls. However, the higher level processes--irregularity detection and attentional focus--functioned in both groups, but less efficiently in patients with schizophrenia. Conclusions: Results demonstrate abnormal auditory temporal processing in schizophrenia. Abnormal performances only in Processes 2 and 3 support and hypothesis of higher level rather than lower level processing deficits in schizophrenia.

Feeling of control of an action after supra and subliminal haptic distortions.

Here we question the mechanisms underlying the emergence of the feeling of control that can be modulated even when the feeling of being the author of ones own action is intact. With a haptic robot, participants made series of vertical pointing actions on a virtual surface, which was sometimes postponed by a small temporal delay (15 or 65 ms). Subjects then evaluated their subjective feeling of control. Results showed that after temporal distortions, the hand-trajectories were adapted effectively but that the feeling of control decreased significantly. This was observed even in the case of subliminal distortions for which subjects did not consciously detect the presence of a distortion. Our findings suggest that both supraliminal and subliminal temporal distortions that occur within a healthy perceptual-motor system impact the conscious experience of the feeling of control of self-initiated motor actions.

SELECTING ONE OF TWO REGULAR SOUND SEQUENCES: PERCEPTUAL AND MOTOR EFFECTS OF TEMPO ','

This study assessed the influence of tempo on selecting a sound sequence. In Exp. 1, synchronization with one of the two regular subsequences in a complex sequence was measured. 30 participants indicated a preference for the fastest subsequence when subsequences were in a slow tempo range (≥ 500 msec. IOI), and with the slower subsequence when they were in the fast tempo range (≤ 300 msec. IOI). These results were replicated using a perceptual task (Exp. 2 and 3) in which the 30 listeners had to detect a temporal irregularity in one of the two subsequences. Detection was better when the temporal irregularity was in the fastest subsequence than in the slowest one when the complex sequence was in a slow tempo range (≥ 500 msec. IOI) and the reverse was obtained when the complex sequence was in a fast tempo range (≤ 180 msec. IOI). These results have implications for design of auditory alarms.

Effect of emotions in a lexical decision task a diffusion model analysis

This study measured the effect of emotional states on lexical decision task performance and investigated which underlying components (physiological, attentional orienting, executive, lexical, and/or strategic) are affected. We did this by assessing participants’ performance on a lexical decision task, which they completed before and after an emotional state induction task. The sequence effect, usually produced when participants repeat a task, was significantly smaller in participants who had received one of the three emotion inductions (happiness, sadness, embarrassment) than in control group participants (neutral induction). Using the diffusion model (Ratcliff, 1978) to resolve the data into meaningful parameters that correspond to specific psychological components, we found that emotion induction only modulated the parameter reflecting the physiological and/or attentional orienting components, whereas the executive, lexical, and strategic components were not altered. These results suggest that emotional states have an impact on the low-level mechanisms underlying mental chronometric tasks.

Perceptual encoding of fingerspelled and printed alphabet by deaf signers: An fMRI study

We measured brain activation during the perception of fingerspelled letters, printed letters, and abstract shapes (control condition) in six congenitally, profoundly deaf signers and six normal hearing subjects. Normal hearing subjects showed essentially extrastriate activation in the fingerspelled letters and printed letters conditions whereas deaf subjects showed activation of a broader network in printed letters and fingerspelled conditions, comprising supplementary frontal and posterior areas, and the supramarginal gyrus (Brodmann Area 6). These results suggest that, on one hand, different cerebral areas in deaf and hearing subjects mediate processing of printed letters and, on the other hand, common cerebral areas are activated in deaf signers when they are engaged in processing fingerspelled or printed letters.