Blending into the Crowd: Electrophysiological Evidence of Gestalt Perception of a Human Dyad.

Human faces and bodies are environmental stimuli of special importance that the brain processes with selective attention and a highly specialized visual system. It has been shown recently that the human brain also has dedicated networks for perception of pluralities of human bodies in synchronous motion or in face-to-face interaction. Here we show that a plurality of human bodies that are merely in close spatial proximity are automatically integrated into a coherent perceptual unit. We used an EEG frequency tagging technique allowing the dissociation of the brain activity related to the component parts of an image from the activity related to the global image configuration. We presented to participants images of two silhouettes flickering at different frequencies (5.88 vs. 7.14 Hz). Clear response at these stimulation frequencies reflected response to each part of the dyad. An emerging intermodulation component (7.14 + 5.88 = 13.02 Hz), a nonlinear response regarded as an objective signature of holistic representation, was significantly enhanced in the (typical) upright relative to an (altered) inverted position. Moreover, the inversion effect was significant for the intermodulation component but not for the stimulation frequencies, suggesting a trade-off between the processing of the global dyad configuration and that of the structural properties of the dyad elements. Our results show that when presented with two humans merely in close proximity the perceptual visual system will bind them. Hence the perception of the human form might be of a fundamentally different nature when it is part of a plurality.

Explicit access to phonetic representations in 3-month-old infants.

Preverbal infants are particularly good at discriminating syllables that differ by a single phoneme but do they perceive syllables as a whole unit or can they become aware of the underlying phonemes if their attention is attracted to the relevant level of analysis? We trained 3-month-old infants to pair two consonants, co-articulated with different vowels, with two visual shapes. Using event-related potentials, we showed that infants generalize the learned associations to new syllables with respect to the training phase. The systematic pairing of a visual label with a phonetic category is rapidly learned in a few trials, suggesting that phonemes are natural categories for infants but also that phonetic representations are accessible to internal operations outside the linguistic system. Hence, the possibility of an explicit access to the phonetic level, which is the main process underlying alphabetic reading system, is grounded in the early faculties of the human infant.

Time dependency of the SNARC effect for different number formats: evidence from saccadic responses.

In line with the suggestion that the strength of the spatial numerical association of response codes (SNARC) effect was time dependent, the aim of the present study was to assess whether the association strength depends on the processing time of numerical quantity and/or of the time to initiate responses. More specifically, we examined whether and how the SNARC effect could be modulated by number format and effector type. Experiment 1 compared the effect induced by Arabic numbers and number words on the basis of saccadic responses in a parity judgment task. Indeed, previous studies have shown that Arabic numbers lead to faster processing than number words. The results replicated the SNARC effect with Arabic numbers, but not with number words. Experiment 2 was similar to Experiment 1, but this time manual responses (i.e., responses far slower than saccadic ones) were recorded. A strong SNARC effect was observed for both number formats. Further analyses revealed a correlation between mean individual response times and the strength of the SNARC effect. We proposed that the initiation times for saccadic responses may be too short for the SNARC effect to appear, in particular with the written number format for which activation of magnitude takes time. We conclude in terms of time variations resulting from processing specificities related with number format, effector type and also individual reaction and processing speed.

Electrophysiological evidence of phonetic normalization across coarticulation in infants.

The auditory neural representations of infants can easily be studied with electroencephalography using mismatch experimental designs. We recorded high-density event-related potentials while 3-month-old infants were listening to trials consisting of CV syllables produced with different vowels (/bX/ or /gX/). The consonant remained the same for the first three syllables, followed (or not) by a change in the fourth position. A consonant change evoked a significant difference around the second auditory peak (400-600 ms) relative to control trials. This mismatch response demonstrates that the infants robustly categorized the consonant despite coarticulation that blurs the phonetic cues, and at an age at which they do not produce these consonants themselves. This response was obtained even when infants had no visual articulatory information to help them to track the consonant repetition. In combination with previous studies establishing categorical perception and normalization across speakers, this result demonstrates that preverbal infants already have abstract phonetic representation integrating over acoustical features in the first months of life.

Suprasegmental information affects processing of talking faces at birth.

From birth, newborns show a preference for faces talking a native language compared to silent faces. The present study addresses two questions that remained unanswered by previous research: (a) Does the familiarity with the language play a role in this process and (b) Are all the linguistic and paralinguistic cues necessary in this case? Experiment 1 extended newborns' preference for native speakers to non-native ones. Given that fetuses and newborns are sensitive to the prosodic characteristics of speech, Experiments 2 and 3 presented faces talking native and nonnative languages with the speech stream being low-pass filtered. Results showed that newborns preferred looking at a person who talked to them even when only the prosodic cues were provided for both languages. Nonetheless, a familiarity preference for the previously talking face is observed in the "normal speech" condition (i.e., Experiment 1) and a novelty preference in the "filtered speech" condition (Experiments 2 and 3). This asymmetry reveals that newborns process these two types of stimuli differently and that they may already be sensitive to a mismatch between the articulatory movements of the face and the corresponding speech sounds.

Early word segmentation in infants acquiring Parisian French: task-dependent and dialect-specific aspects.

Six experiments explored Parisian French-learning infants' ability to segment bisyllabic words from fluent speech. The first goal was to assess whether bisyllabic word segmentation emerges later in infants acquiring European French compared to other languages. The second goal was to determine whether infants learning different dialects of the same language have partly different segmentation abilities, and whether segmenting a non-native dialect has a cost. Infants were tested on standard European or Canadian French stimuli, in the word-passage or passage-word order. Our study first establishes an early onset of segmentation abilities: Parisian infants segment bisyllabic words at age 0;8 in the passage-word order only (revealing a robust order of presentation effect). Second, it shows that there are differences in segmentation abilities across Parisian and Canadian French infants, and that there is a cost for cross-dialect segmentation for Parisian infants. We discuss the implications of these findings for understanding word segmentation processes.

Transitional probabilities and positional frequency phonotactics in a hierarchical model of speech segmentation.

The present study explored the influence of a new metrics of phonotactics on adults' use of transitional probabilities to segment artificial languages. We exposed French native adults to continuous streams of trisyllabic nonsense words. High-frequency words had either high or low congruence with French phonotactics, in the sense that their syllables had either high or low positional frequency in French trisyllabic words. At test, participants heard low-frequency words and part-words, which differed in their transitional probabilities (high for words, low for part-words) but were matched for frequency and phonotactic congruency. Participants' preference for words over part-words was found only in the high-congruence languages. These results establish that subtle phonotactic manipulations can influence adults' use of transitional probabilities to segment speech and unambiguously demonstrate that this prior knowledge interferes directly with segmentation processes, in addition to affecting subsequent lexical decisions. Implications for a hierarchical theory of segmentation cues are discussed.