Nicolas Dupuis-Roy

Uncovering gender discrimination cues in a realistic setting

Which face cues do we use for gender discrimination? Few studies have tried to answer this question and the few that have tried typically used only a small set of grayscale stimuli, often distorted and presented a large number of times. Here, we reassessed the importance of facial cues for gender discrimination in a more realistic setting. We applied Bubbles-a technique that minimizes bias toward specific facial features and does not necessitate the distortion of stimuli-to a set of 300 color photographs of Caucasian faces, each presented only once to 30 participants. Results show that the region of the eyes and the eyebrows-probably in the light-dark channel-is the most important facial cue for accurate gender discrimination; and that the mouth region is driving fast correct responses (but not fast incorrect responses)-the gender discrimination information in the mouth region is concentrated in the red-green color channel. Together, these results suggest that, when color is informative in the mouth region, humans use it and respond rapidly; and, when its not informative, they have to rely on the more robust but more sluggish luminance information in the eye-eyebrow region.

Perceptual learning without signal.

Perceptual learning is characterized by an improvement in a perceptual task following practice. Several studies have demonstrated that top-down processes, such as attention and task-related expectations, can be necessary components of perceptual learning [Ahissar & Hochstein, 1993, 2000, 2002; Fahle & Morgan, 1996; Seitz, Lefebvre, Watanabe, & Jolicoeur, 2005; Seitz, Nanez, Holloway, Koyama, & Watanabe, 2005; Seitz & Watanabe, 2003; Shiu & Pashler, 1992]. Here, we report an experiment that isolated top-down processes in perceptual learning, using a variant of the Gosselin and Schyns (1992) no-signal procedure. Results indicate that top-down processes can be sufficient to produce substantial, possibly long-lasting and rotation-invariant perceptual learning.

Reading laterally: The cerebral hemispheric use of spatial frequencies in visual word recognition

It is generally accepted that the left hemisphere (LH) is more capable for reading than the right hemisphere (RH). Left hemifield presentations (initially processed by the RH) lead to a globally higher error rate, slower word identification, and a significantly stronger word length effect (i.e., slower reaction times for longer words). Because the visuo-perceptual mechanisms of the brain for word recognition are primarily localized in the LH (Cohen et al., 2003), it is possible that this part of the brain possesses better spatial frequency (SF) tuning for processing the visual properties of words than the RH. The main objective of this study is to determine the SF tuning functions of the LH and RH for word recognition. Each word image was randomly sampled in the SF domain using the SF bubbles method (Willenbockel et al., 2010) and was presented laterally to the left or right visual hemifield. As expected, the LH requires less visual information than the RH to reach the same level of performance, illustrating the well-known LH advantage for word recognition. Globally, the SF tuning of both hemispheres is similar. However, these seemingly identical tuning functions hide important differences. Most importantly, we argue that the RH requires higher SFs to identify longer words because of crowding.

The event-related potential elicited by taste-visual cross-modal interference

Sixteen healthy subjects took part in this event-related potentials (ERPs) study aimed at investigating the neural response of the taste-visual cross-modal pairing. An interference effect was observed at the behavioral level: the mismatched condition was performed more slowly than the matched condition. ERP analyses revealed a more negative component between 400 and 600 ms in the mismatched condition than in the matched condition. Dipole source analysis of the difference wave (mismatched minus matched) indicated that two generators localized in prefrontal cortex (PFC) and posterior cingulate cortex (PCC) contributed to this cross-modal interference effect. These results provided the electrophysiological evidence of interference during the extraction of taste information from memory and conflict control during the incongruent taste-visual information processing.

Real-World Interattribute Distances Lead to Inefficient Face Gender Categorization

The processing of interattribute distances is believed to be critical for upright face categorization. A recent study by Taschereau-Dumouchel, Rossion, Schyns, and Gosselin (2010) challenged this idea by showing that participants were nearly at chance when asked to identify faces on the sole basis of real-world interattribute distances, while they were nearly perfect when all other facial cues were shown. However, it remains possible that humans are highly tuned to interattribute distances but that the information conveyed by these cues is scarce. We tested this hypothesis by contrasting the efficiencies-a measure of performance that factors out task difficulty-of 60 observers in 6 face gender categorization tasks. Our main finding is that efficiencies for faces that varied only in terms of their interattribute distances were an order of magnitude lower than efficiencies for faces that varied in all respects, except their interattribute distances, or in all respects. These results provide a definitive blow to the idea that real-world interattribute distances are critical for upright face processing. (PsycINFO Database Record (c) 2014 APA, all rights reserved).

Neural correlates of the modified Stroop effect in post-traumatic stress disorder: an event-related potential study.

Previous studies have provided electrophysiological evidence for attentional abnormalities in patients with post-traumatic stress disorder (PTSD). The present study examined the electrophysiological activity of trauma-exposed patients with or without a PTSD during a modified Stroop task. The PTSD group showed a reduced P2 and P3 amplitude relative to the non-PTSD group under both the earthquake-related and earthquake-unrelated words conditions. Importantly, the earthquake-related words elicited a greater P3 amplitude (350–450 ms after stimulus) than did unrelated words in the non-PTSD group, whereas no significant difference was found in the PTSD group. This indicates that PTSD patients had some attention deficits compared with non-PTSD individuals, and that these attention deficits were not just limited to earthquake-related words.

Time course of the use of chromatic and achromatic facial information for sex categorization

The most useful facial features for sex categorization are the eyes, the eyebrows, and the mouth. Dupuis-Roy et al. reported a large positive correlation between the use of the mouth region and rapid correct answers [Journal of Vision 9 (2009) 1-8]. Given the chromatic information in this region, they hypothesized that the extraction of chromatic and achromatic cues may have different time courses. Here, we tested this hypothesis directly: 110 participants categorized the sex of 300 face images whose chromatic and achromatic content was partially revealed through time (200 ms) and space using randomly located spatio-temporal Gaussian apertures (i.e. the Bubbles technique). This also allowed us to directly compare, for the first time, the relative importance of chromatic and achromatic facial cues for sex categorization. Results showed that face-sex categorization relies mostly on achromatic (luminance) information concentrated in the eye and eyebrow regions, especially the left eye and eyebrow. Additional analyses indicated that chromatic information located in the mouth/philtrum region was used earlier-peaking as early as 35 ms after stimulus onset-than achromatic information in the eye regions-peaking between 165 and 176 ms after stimulus onset-as was speculated by Dupuis-Roy et al. A non-linear analysis failed to support Yip and Sinhas proposal that processing of chromatic variations can improve subsequent processing of achromatic spatial cues, possibly via surface segmentation [Perception 31 (2002) 995-1003]. Instead, we argue that the brain prioritizes chromatic information to compensate for the sluggishness of chromatic processing in early visual areas, and allow chromatic and achromatic information to reach higher-level visual areas simultaneously.

The Neural Basis of Taste-visual Modal Conflict Control in Appetitive and Aversive Gustatory Context

The functional magnetic resonance imaging (fMRI) technique was used to investigate brain activations related to conflict control in a taste-visual cross-modal pairing task. On each trial, participants had to decide whether the taste of a gustatory stimulus matched or did not match the expected taste of the food item depicted in an image. There were four conditions: Negative match (NM; sour gustatory stimulus and image of sour food), negative mismatch (NMM; sour gustatory stimulus and image of sweet food), positive match (PM; sweet gustatory stimulus and image of sweet food), positive mismatch (PMM; sweet gustatory stimulus and image of sour food). Blood oxygenation level-dependent (BOLD) contrasts between the NMM and the NM conditions revealed an increased activity in the middle frontal gyrus (MFG) (BA 6), the lingual gyrus (LG) (BA 18), and the postcentral gyrus. Furthermore, the NMM minus NM BOLD differences observed in the MFG were correlated with the NMM minus NM differences in response time. These activations were specifically associated with conflict control during the aversive gustatory stimulation. BOLD contrasts between the PMM and the PM condition revealed no significant positive activation, which supported the hypothesis that the human brain is especially sensitive to aversive stimuli. Altogether, these results suggest that the MFG is associated with the taste-visual cross-modal conflict control. A possible role of the LG as an information conflict detector at an early perceptual stage is further discussed, along with a possible involvement of the postcentral gyrus in the processing of the taste-visual cross-modal sensory contrast.

The role of interattribute distances in face recognition and their relation to holistic processing

To understand the impact of interattribute distances (IADs) in face recognition, we correlated the performance of 42 participants in the Cambridge Face Memory Test (CFMT) and in the Face Composite Task to their sensitivity to IADs, as indexed by three novel tasks. In the first task, participants needed to adjust the length of an horizontal line to match the interocular distance (IOD) of a briefly presented face (1000ms). Face stimuli were shown in various sizes. White positional noise with constant energy was added independently to the xy-coordinates of the left eye, and the y-coordinates of the nose, the mouth and the left brow. The right eye and brow were kept symmetrical to the left ones. Performance was measured as the correlation between the adjusted length and the veridical IOD. In the two other tasks, two face stimuli were shown successively for 500ms, and participants had to decide if they were identical or different. The stimuli were created the same way as in the first task, except that in 50% of the trials, both faces had identical IOD (second task) or identical IADs (third task). The level of noise was adjusted to maintain an accuracy of 75% and was taken as a index of performance. The third task was significantly correlated with the CFMT (r=-.4, p< 0.01), suggesting that it reflects global visual processing capabilities in face identification. However, no significant correlation was found between our three tasks and the five indexes of the Composite Face Effect (CFE; DeGutis, et al, 2013; Konar et al., 2010; Richler, et al. 2011). This suggests that global sensitivity to IADs and the capacity to use IOD while ignoring other IADs, are not associated with holistic face processing. Specific links between the CFE and facial scaling will be tested with models on the positional noise. Meeting abstract presented at VSS 2015.

Exposure to traumatic experiences is associated with abnormal neural mechanism during charitable donation

Previous studies suggested that posttraumatic stress disorder (PTSD) might be associated with dysfunctional reward processing. At present, little is known about the neural mechanisms of reward-related processing during a charitable donation task in trauma survivors who do not go on to develop PTSD. We used functional magnetic resonance imaging (fMRI) to investigate the neural basis of charitable donation in non-PTSD survivors of the Sichuan earthquake. Results showed that activations in the striatum of trauma survivors were reduced in both the low donation (donated a small amount to the Red Cross) and the high donation conditions (donated a large amount to the Red Cross) compared with the healthy controls. Furthermore, the trauma survivors also exhibited less activity in the insula than the healthy controls in the high donation condition. These findings suggest that abnormal reward-related activations might be associated with dysfunctions in the reward pathway of trauma survivors. Also, we discuss the possibility that traumatic experiences attenuate the reactivity of reward-related brain areas to positive emotions (as induced by advantageous donations).