Sensory and cognitive mechanisms allow stimuli to be perceived with properties relating to sight, sound, touch, etc, and ensure, for example, that visual properties are perceived as visual experiences, rather than sounds, tastes, smells, etc. Theories of normal development can be informed by cases where this modularity breaks down, in a condition known as synaesthesia. Conventional wisdom has held that this occurs extremely rarely (0.05% of births) and affects women more than men. Here we present the first test of synaesthesia prevalence with sampling that does not rely on self-referral, and which uses objective tests to establish genuineness. We show that (a) the prevalence of synaesthesia is 88 times higher than previously assumed, (b) the most common variant is coloured days, (c) the most studied variant (grapheme - colour synaesthesia)—previously believed most common—is prevalent at 1%, and (d) there is no strong asymmetry in the distribution of synaesthesia across the sexes. Hence, we suggest that female biases reported earlier likely arose from (or were exaggerated by) sex differences in self-disclosure.

Abstract& The range of specificity and the response properties of the extrastriate face area were investigated by comparing the N170 event-related potential (ERP) component elicited by photographs of natural faces, realistically painted portraits, sketches of faces, schematic faces, and by nonface meaningful and meaningless visual stimuli. Results showed that the N170 distinguished between faces and nonface stimuli when the concept of a face was clearly rendered by the visual stimulus, but it did not distinguish among different face types: Even a schematic face made from simple line fragments triggered the N170. However, in a second experiment, inversion seemed to have a different effect on natural faces in which face components were available and on the pure gestalt-based schematic faces: The N170 amplitude was enhanced when natural faces were presented upside down but reduced when schematic faces were inverted. Inversion delayed the N170 peak latency for both natural and schematic faces. Together, these results suggest that early face processing in the human brain is subserved by a multiple-component neural system in which both whole-face configurations and face parts are processed. The relative involvement of the two perceptual processes is probably determined by whether the physiognomic value of the stimuli depends upon holistic configuration, or whether the individual components can be associated with faces even when presented outside the face context. &

What aspects of face processing are impaired in developmental prosopagnosia?Le Grand, R.; Cooper, P.A.; Mondloch, C.J.; Lewis, T.L.; Sagiv, M.; de Gelder, Bea; Maurer, D. Published in: Brain and Cognition Document version:Publisher's PDF, also known as Version of record Publication date: 2006Link to publication Citation for published version (APA):Le Grand, R., Cooper, P. A., Mondloch, C. J., Lewis, T. L., Sagiv, M., de Gelder, B., & Maurer, D. (2006). What aspects of face processing are impaired in developmental prosopagnosia? Brain and Cognition, 61(2), 139-158. General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.-Users may download and print one copy of any publication from the public portal for the purpose of private study or research -You may not further distribute the material or use it for any profit-making activity or commercial gain -You may freely distribute the URL identifying the publication in the public portal Take down policyIf you believe that this document breaches copyright, please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractDevelopmental prosopagnosia (DP) is a severe impairment in identifying faces that is present from early in life and that occurs despite no apparent brain damage and intact visual and intellectual function. Here, we investigated what aspects of face processing are impaired/ spared in developmental prosopagnosia by examining a relatively large group of individuals with DP (n D 8) using an extensive battery of well-established tasks. The tasks included measures of sensitivity to global motion and to global form, detection that a stimulus is a face, determination of its sex, holistic face processing, processing of face identity based on features, contour, and the spacing of features, and judgments of attractiveness. The DP cases showed normal sensitivity to global motion and global form and performed normally on our tests of face detection and holistic processing. On the other tasks, many DP cases were impaired but there was no systematic pattern. At least half showed deWcits in processing of facial identity based on either the outer contour or spacing of the internal features, and/or on judgments of attractiveness. Three of the eight were impaired in processing facial identify based on the shape of internal features. The results show that DP is a heterogeneous condition and that impairment in recognizing faces cannot be predicted by poor performance on any one measure of face processing.

To compare neural activity produced by visual events that escape or reach conscious awareness, we used event-related MRI and evoked potentials in a patient who had neglect and extinction after focal right parietal damage, but intact visual fields. This neurological disorder entails a loss of awareness for stimuli in the field contralateral to a brain lesion when stimuli are simultaneously presented on the ipsilateral side, even though early visual areas may be intact, and single contralateral stimuli may still be perceived. Functional MRI and event-related potential study were performed during a task where faces or shapes appeared in the right, left, or both fields. Unilateral stimuli produced normal responses in V1 and extrastriate areas. In bilateral events, left faces that were not perceived still activated right V1 and inferior temporal cortex and evoked nonsignificantly reduced N1 potentials, with preserved face-specific negative potentials at 170 ms. When left faces were perceived, the same stimuli produced greater activity in a distributed network of areas including right V1 and cuneus, bilateral fusiform gyri, and left parietal cortex. Also, effective connectivity between visual, parietal, and frontal areas increased during perception of faces. These results suggest that activity can occur in V1 and ventral temporal cortex without awareness, whereas coupling with dorsal parietal and frontal areas may be critical for such activity to afford conscious perception. R ight parietal damage may cause a loss of awareness for contralateral (left) sensory inputs, such as hemispatial neglect and extinction (1-3). Visual extinction is the failure to perceive a stimulus in the contralesional field when presented together with an ipsilesional stimulus (bilateral simultaneous stimulation, BSS), even though occipital visual areas are intact and unilateral contralesional stimuli can be perceived when presented alone. It reflects a deficit of spatial attention toward the contralesional side, excluding left inputs from awareness in the presence of competing stimuli (2, 3). Spatial attention involves a complex neural network centered on the right parietal lobe (4, 5), but how parietal and related areas interact with sensory processing in distant cortices is largely unknown.Here we combined event-related functional MRI (fMRI) and event-related potentials (ERPs) to study the regional pattern and temporal course of brain activity produced by seen and unseen stimuli in a patient with chronic neglect and extinction caused by parietal damage. In keeping with intact early visual areas in such patients, behavioral studies suggest that some residual processing may still occur for contralesional stimuli without attention, or without awareness, including ''preattentive'' grouping (e.g., refs. 6 and 7) and semantic priming (e.g., ref. 8). It has been speculated (3, 9) that such effects might relate to separate cortical visual streams, with temporal areas extracting object features for identification, and parietal areas encoding spatial...

No abstract

No abstract

The neural mechanisms involved in binding features such as shape and color are a matter of some debate. Does accurate binding rely on spatial attention functions of the parietal lobe or can it occur without attentional input? One extraordinary phenomenon that may shed light on this question is that of chromatic-graphemic synesthesia, a rare condition in which letter shapes evoke color perceptions. A popular suggestion is that synesthesia results from cross-activation between different functional regions (e.g., between shape and color areas of the ventral pathway). Under such conditions binding may not require parietal involvement and could occur preattentively. We tested this hypothesis in two synesthetes who perceived grayscale letters and digits in color. We found no evidence for preattentive binding using a visual search paradigm in which the target was a synesthetic inducer. In another experiment involving color judgments, we show that the congruency of target color and the synesthetic color of irrelevant digits modulates performance more when the digits are included within the attended region of space. We propose that the mechanisms giving rise to this type of synesthesia appear to follow at least some principles of normal binding, and even synesthetic binding seems to require attention.

Accumulated evidence from electrophysiology and neuroimaging suggests that face perception involves extrastriate visual mechanisms specialized in processing physiognomic features and building a perceptual representation that is categorically distinct and can be identified by face-recognition units. In the present experiment, we recorded event-related brain potentials in order to explore possible contextual influences on the activity of this perceptual mechanism. Subjects werefirst exposed to pairs of small shapes, which did not elicit any face-specific brain activity. The same stimuli, however, elicitedface-specific brain activity after subjects saw them embedded in schematic faces, which probably primed the subjects to interpret the shapes as schematic eyes. No face-specific activity was observed when objects rather than faces were used to form the context. We conclude that the activity of face-specific extrastriate perceptual mechanisms can be modulated by contextual constraints that determine the significance of the visual input.