Le cerveu à l`école

Conference given outside the academic context (2011)

Scrambling horizontal face structure: behavioral and electrophysiogical evidence for a tuning of visual face processing to horizontal information

Poster (2011, August)

Filtering faces to remove all but the horizontal information largely preserves behavioral signatures of face-specific processing, including the face inversion effect (FIE). Conversely, preserving only ... [more ▼]

Filtering faces to remove all but the horizontal information largely preserves behavioral signatures of face-specific processing, including the face inversion effect (FIE). Conversely, preserving only vertical information abolishes this effect. In contrast to previous studies which used filtering, the present studies manipulated orientation content of face images by randomizing Fourier phase spectrum in a narrow horizontal orientation band (H-randomization) or vertical orientation band (V-randomization). Phase-randomization was performed on face images in which spatial frequency amplitude spectrum (SF-AS) was either left unaltered or equalized across all SF orientations. We further investigated the time course of horizontal tuning using event-related potentials (ERP). We observed that (i) upright faces were best discriminated when the horizontal structure was preserved (ie V-randomization) compared to H-randomization; (ii) this phase-randomization effect was eliminated by inversion, resulting in (iii) a smaller FIE for H-randomized than V-randomized faces. This pattern was still present but was less consistent when SF-AS was equalized across SF orientations, suggesting that SF-AS in horizontal orientation contributes to the horizontal tuning of face perception. ERP evidence of horizontal tuning for upright face processing was observed in the N170 time-window, a well-known face-sensitive electrophysiological component. The N170 was delayed for H-randomized compared to V-randomized faces. Additionally, and in line with behavioural data, face inversion increased N170 latency to a smaller extent for H-randomized compared to V-randomized. Altogether, our findings indicate that horizontal tuning is a robust property of face perception that arises early in high-level visual cortex. [less ▲]

Interactions between number and space processing in adults with dyscalculia

Poster (2011, May 27)

A large body of evidence indicates clear relationships between number and space processing in healthy and brain-damaged adults, as well as in children. The present paper addressed this issue regarding ... [more ▼]

A large body of evidence indicates clear relationships between number and space processing in healthy and brain-damaged adults, as well as in children. The present paper addressed this issue regarding atypical math development. Adults with a diagnosis of dyscalculia (DYS) during childhood were compared to adults with average or high abilities in mathematics across two bisection tasks. Participants were presented with Arabic number triplets and had to judge either the number magnitude or the spatial location of the middle number relative to the two outer numbers. For the numerical judgment, adults with DYS were slower than both groups of control peers. They were also more strongly affected by the factors related to number magnitude such as the range of the triplets or the distance between the middle number and the real arithmetical mean. By contrast, adults with DYS were as accurate and fast as adults who never experienced math disability when they had to make a spatial judgment. Moreover, number-space congruency affected performance similarly in the three experimental groups. These findings support the hypothesis of a deficit of number magnitude representation in DYS with a relative preservation of some spatial mechanisms in DYS. Results are discussed in terms of direct and indirect number-space interactions. [less ▲]

Contribution of Spatial Frequency and Orientation to upright and inverted face perception

Poster (2011, May)

It was recently shown that expert face perception relies on the extraction of horizontally oriented visual cues. Picture-plane inversion was found to eliminate horizontal, suggesting that this tuning ... [more ▼]

It was recently shown that expert face perception relies on the extraction of horizontally oriented visual cues. Picture-plane inversion was found to eliminate horizontal, suggesting that this tuning contributes to the specificity of face processing. The present experiments sought to determine the spatial frequency (SF) scales supporting the horizontal tuning of face perception. Participants were instructed to match upright and inverted faces that were filtered both in the frequency and orientation domains. Faces in a pair contained horizontal or vertical ranges of information in low, middle, or high SF (LSF, MSF, or HSF). Our findings confirm that upright (but not inverted) face perception is tuned to horizontal orientation. Horizontal tuning was the most robust in the MSF range, next in the HSF range, and absent in the LSF range. Moreover, face inversion selectively disrupted the ability to process horizontal information in MSF and HSF ranges. This finding was replicated even when task difficulty was equated across orientation and SF at upright orientation. Our findings suggest that upright face perception is tuned to horizontally oriented face information carried by intermediate and high SF bands. They further indicate that inversion alters the sampling of face information both in the orientation and SF domains. [less ▲]

Shifts of spatial attention cued by irrelevant numbers: Electrophysiological evidence from a target discrimination task

Poster (2011, April)

Fischer et al. demonstrated that a centrally presented number can shift attention to the left/right when its magnitude is small/large. Two electrophysiological studies described these attentional effects ... [more ▼]

Fischer et al. demonstrated that a centrally presented number can shift attention to the left/right when its magnitude is small/large. Two electrophysiological studies described these attentional effects as event-related potentials (ERPs) at centro-parietal sites. Since both studies used target detection tasks, it remains currently unknown whether similar results would be obtained with a discrimination task. We used ERPs to test whether digit cues also induce attention shifts when participants perform a feature-discrimination task on targets. ERPs were recorded whereas subjects discriminated the colour of lateral targets that were preceded by a central non-predictive digit. Analysis of cue-locked controlateral vs. ipsilateral ERP activity showed the emergence of early preparatory attention-directing components in parietal and frontal regions. Moreover, target-locked P1 components at occipito-parietal sites were significantly modulated by digit magnitude-target side congruency. These results demonstrate that irrelevant digit cues also bias sensory processing when embedded in a feature-discrimination task. [less ▲]

When numbers act as attentional cues: behavioral and fMRI investigations

Poster (2011, February 11)

The SNARC effect – Does it depend on the level of mathematical training?

Poster (2011)

Behavioural studies show a relation between numbers and space (DeHevia et al., 2008). One instance of this link is the SNARC (Spatial Numerical Association of Response Codes) effect, consisting in faster ... [more ▼]

Behavioural studies show a relation between numbers and space (DeHevia et al., 2008). One instance of this link is the SNARC (Spatial Numerical Association of Response Codes) effect, consisting in faster reaction times responding to small/large digits with the left/right hand respectively (Dehaene et al. 1993). The SNARC effect has often been replicated, but it is also characterized by high inter-subject variability (Wood et al. 2006a,b). Although differences in mathematical skills are an obvious candidate source for SNARC variability, this variable has not yet been explored systematically. While in their seminal study Dehaene and colleagues had included two groups of participants differing in their field of study (science vs. literature), the differences in SNARC effect strengths indicated by the result figures were not tested formally (see also Fischer and Rottmann (2005)). The present study aims to assess the influence of mathematical training, as instantiated by the enrollment in study fields characterized by distinct levels of mathematical requirements, on the SNARC effect. We only included students of either a subject with a strong mathematical focus (e.g. mathematics, computer sciences), or no mathematical requirements at all (e.g. literature, philosophy). Results (N=36; 18/group) yielded a significant overall SNARC effect, i.e. interaction between digit magnitude and response side [F(1,35)=9.51; p=0.004], but no influence of study group on this interaction [F(1,35)=0.92; p=0.345]. Interestingly though, including gender in the ANOVA yielded a significant four-way interaction [F(1,35)=6.34; p=0.017]. These results replicate previous findings in children (Schweiter et al. 2005), interpreted as gender-related differences in mental strategy use. [less ▲]

Facilitation and inhibition of return using numbers as attentional cues

Poster (2011)

Behavioural studies have shown a relation between numbers and space (DeHevia et al., 2008). Fischer and colleagues (2003) showed that digits can act as central spatial cues in a target detection task ... [more ▼]

Behavioural studies have shown a relation between numbers and space (DeHevia et al., 2008). Fischer and colleagues (2003) showed that digits can act as central spatial cues in a target detection task, resulting in shorter reaction times (RT) for left-sided targets when preceded by small numbers and for right-sided targets when preceded by large numbers. This facilitation effect indicates that numbers orient visuo-spatial attention to the left or right hemifield, depending on their magnitude. To date no studies investigated whether this facilitation is followed by inhibition of return at longer intervals, as could be expected with visuo-spatial attention shifts. To this aim, we designed an analogous paradigm to Fischer et al.’s, introducing additional longer intervals. Participants (n=25) were presented a task irrelevant digit (1,2 vs. 8,9) for 400ms and had to detect a brief (100ms) lateral target appearing after a variable interval (100, 250, 500, 750, 1000, 1250ms). A 2x6 repeated measures ANOVA of mean RT, with congruency and interval as within-subject variables yielded a significant interaction (F(5,24)=2.3, p<0.05). As expected, targets were detected faster when appearing in the congruent (small-left, large-right) hemifield after 250ms. Using the regression method proposed by Lorch and Myers (1990), the slope at this interval was significantly negative (t(24)=1.70, p=0.05); indicating a facilitation for the detection of targets in the congruent hemifield) (cf. Fischer et al., 2003). At the 1250ms interval, targets were detected significantly slower when they appeared in the congruent compared to the incongruent hemifield (yielding significantly positive slopes at 1250ms: t(24)=2.68, p=0.007). These findings provide the first evidence that digits not only produce facilitation effects at shorter intervals, but also induce inhibitory effects at longer intervals, confirming the visuo-spatial nature of the attention shifts associated with Arabic digits. [less ▲]

Characterizing the face processing network in the human brain: a large-scale fMRI localizer study

in Journal of Vision (2010), 10(7),

A whole network of brain areas showing larger response to faces than other visual stimuli has been identified in the human brain using fMRI (Sergent, 1992; Haxby, 2000). Most studies identify only a ... [more ▼]

A whole network of brain areas showing larger response to faces than other visual stimuli has been identified in the human brain using fMRI (Sergent, 1992; Haxby, 2000). Most studies identify only a subset of this network, by comparing the presentation of face pictures to all kinds of object categories mixed up (e.g., Kanwisher, 1997), or to scrambled faces (e.g., Ishaï, 2005), using different statistical thresholds. Given these differences of approaches, the (sub)cortical face network can be artificially overextended (Downing & Wiggett, 2008), or minimized in different studies, both at the local (size of regions) and global (number of regions) levels. Here we conducted an analysis of a large set of right-handed subjects (40), tested with a new whole-brain localizer to control for both high-level and low-level differences between faces and objects. Pictures of faces, cars and their phase-scrambled counterparts were used in a 2x2 block design. Group-level (random effect) and single subject (ROI) analyses were made. A conjunction of two contrasts (F-SF and F-C) identified 6 regions: FFA, OFA, amygdala, pSTS, AIT and thalamus. All these regions but the amygdala showed clear right lateralization. Interestingly, the FFA showed the least face-selective response among the cortical face network: it presented a significantly larger response to pictures of cars than scrambled cars [t=9.3, much more than amygdala (t=2.6), AIT (t=2.1) and other regions (NS)], and was also sensitive to low-level properties of faces [SF - SO; t=5.1; NS in other areas]. These observations suggest that, contrary to other areas of the network, including the OFA, the FFA is a region that may contain populations of neurons that are specific to faces intermixed with populations responding more generally to object categories. More generally, this study helps understanding the extent and specificity of the network of (sub)cortical areas particularly involved in face processing. [less ▲]

Cerebral lateralization of the face-cortical network in left-handers: only the FFA does not get it right

in Journal of Vision (2010), 10(7),

Face processing is a function that is highly lateralized in humans, as supported by original evidence from brain lesion studies (Hecaen & Anguerlergues, 1962), followed by studies using divided visual ... [more ▼]

Face processing is a function that is highly lateralized in humans, as supported by original evidence from brain lesion studies (Hecaen & Anguerlergues, 1962), followed by studies using divided visual field presentations (Heller & Levy, 1981), neuroimaging (Sergent et al., 1992) and event-related potentials (Bentin et al., 1996). Studies in non-human primates (Perrett et al., 1988; Zangenehpour & Chaudhuri, 2005), or other mammals (Peirce & Kendrick, 2001) support the right lateralization of the function, which may be related to a dominance of the right hemisphere in global visual processing. However, in humans there is evidence that manual preference may shift or qualify the pattern of lateralization for faces in the visual cortex: face recognition impairments following unilateral left hemisphere brain damage have been found only in a few left-handers (e.g., Mattson et al., 1992; Barton, 2009). Here we measured the pattern of lateralization in the entire cortical face network in right and left-handers (12 subjects in each group) using a well-balanced face-localizer block paradigm in fMRI (faces, cars, and their phase-scrambled versions). While the FFA was strongly right lateralized in right-handers, as described previously, it was equally strong in both hemispheres in left-handers. In contrast, other areas of the face-sensitive network (posterior superior temporal sulcus, pSTS; occipital face area, OFA; anterior infero-temporal cortex, AIT; amygdala) remained identically right lateralized in both left- and right-handers. Accordingly, our results strongly suggest that the face-sensitive network is equally lateralized for left- and right-handers, and thus the face processing is not influenced by handedness. However, the FFA is an important exception since it is right-lateralized for right-handers but its recruitment is more balanced between hemispheres for left-handers. These observations carry important theoretical and clinical implications for the aetiology of brain lateralization depending on the left- or right-handedness and the neuropsychological undertaking of prosopagnosic patients. [less ▲]