TMS over right OFA affects individuation of faces but not of exemplars of objects

In addition to its well-documented role in processing of faces, the occipital face area in the right hemisphere (rOFA) may also play a role in identifying specific individuals within a class of objects. Here we explored this issue by using fMRI-guided TMS. In a first experiment, participants had to judge whether two sequentially presented images of faces or objects represented exactly the same exemplar or two different exemplars of the same class, while receiving online TMS over either the rOFA, the right lateral occipital cortex (rLO) or the Vertex (control). We found that, relative to Vertex, stimulation of rOFA impaired individuation of faces only, with no effect on objects; in contrast, TMS over rLO reduced individuation of objects but not of faces. In a second control experiment participants judged whether a picture representing a fragment of a stimulus belonged or not to the subsequently presented image of a whole stimulus (part-whole matching task). Our results showed that rOFA stimulation selectively disrupted performance with faces, whereas performance with objects (but not with faces) was selectively affected by TMS over rLO. Overall, our findings suggest that rOFA does not contribute to discriminate between exemplars of non-face objects

Investigating the functional roles of occipital face area and lateral occipital cortex with transcranial magnetic stimulation

This thesis investigates the causal role of two extra-striate visual regions, the lateral occipital (LO) cortex and the occipital face area (OFA), in certain visual processes. Firstly, I examined whether these areas are causally implicated in the perception of bilateral visual symmetry. Despite the ubiquitous presence of this feature in the external world, the neural basis underlying its detection is not fully known. In Studies I and II,this issue was explored by disrupting the activity of LO and OFA with fMRI-guided transcranial magnetic stimulation (TMS) while participants discriminated between symmetric and nonsymmetric dot configurations and between perfectly symmetric and normal (i.e. somewhat non symmetric) faces. The results showed that rightOFA plays a causal role in detection of symmetry in both configurations of dots and faces whereas LO exclusively in the former, with the rightLO showing greater involvement relative to the homologous region in the left hemisphere. As symmetry is extracted in a holistic manner (i.e. through a parallel global analysis of the stimulusrather than via a serial point-by-point comparisonof the local elements), Study III examined whether rightOFA is involved, more generally, in visual detection based on holistic encoding and, if so, whether its role is restricted to faces or extends also to non-face stimuli. To examine this issue, rightOFA and rightLO were stimulated with fMRI-guided TMS meanwhile participants were asked to detect Mooney faces and non-face images, a class of stimuli which are known to be perceived through holistic processes. The results showed that rightOFA is causally involved in detection of both Mooney faces and objects. Taken together, this thesis sheds new light on the functions of LO and OFA in visual perception. Firstly, it demonstrates that both of these regions are causally involved in holistic processes, including detection of symmetry. Secondly, it is shownthat OFA s role in holistic processing extends to both face and non-face stimuli, suggesting that this region is not strictly face-selective.Tässä väitöskirjatyössä tutkitaan kahden myöhäisen näköaivokuoren alueen (lateral occipital cortex (LO) ja occipital face area (OFA)) kausaalista roolia tietyissä visuaalisissa prosesseissa. Ensiksi tutkittiin, osallistuvatko nämä alueet kausaalisesti bilateraalisen symmetrian havaitsemiseen. Huolimatta siitä, että symmetriaa on läsnä kaikkialla ympäröivässä maailmassa, sen havaitsemisen hermostollinen perusta ei ole vielä täysin tunnettu. Osatutkimuksissa I ja II asiaa tutkittiin häiritsemällä koehenkilöiden aivojen aktiivisuutta alueilla LO ja OFA fMRI-ohjatun trankraniaalisen magneettistimulaation (TMS) avulla, samalla kun he erottelivat symmetrisiä ja epäsymmetrisiä pistekuvioita sekä täysin symmetrisiä ja normaaleja (jonkin verran epäsymmetrisiä) kasvoja toisistaan. Tulokset osoittivat, että oikeanpuoleisella OFA:lla on kausaalinen rooli sekä pistekuvioiden että kasvojen symmetrian havaitsemisessa, kun taas LO:lla pelkästään edellisessä. Oikeanpuoleisen LO:n osallistumisen havaittiin olevan lisäksi voimakkaampaa suhteessa vastaavaan alueeseen vasemmassa aivopuoliskossa. Koska symmetria havaitaan holistisesti (havaitun ärsykkeen globaalin rinnakkaisen analyysin perusteella paikallisen piste pisteeltä vertailun sijaan), III osatyössä selvitettiin osallistuuko oikeanpuoleinen OFA yleisemmin visuaaliseen havaitsemiseen holistiseen enkoodaukseen perustuen, ja onko sen rooli rajoittunut pelkästään kasvoärsykkeisiin. Tämän tutkimiseksi oikeanpuoleista OFA:ta ja LO:ta stimuloitiin fMRI-ohjatulla TMS:lla koehenkilöiden tarkkaillessa n.k. Mooney kasvoja ja kuvia, joita molempia tiedetään prosessoitavan holistisesti. Tulokset osoittivat, että oikeanpuoleinen OFA osallistuu kausaalisesti sekä Mooney kasvojen että objektien tarkasteluun. Tämä väitöskirja laajentaa ymmärrystä LO ja OFA alueiden toiminnasta visuaalisessa havaitsemisessa. Ensiksi, se demonstroi, että molemmat näistä alueista osallistuvat kausaalisesti holistiseen prosessointiin, sisältäen myös symmetrian havaitsemisen. Toiseksi, työssä osoitetaan, että OFA:n rooli holistisessa prosessoinnissa käsittää sekä kasvo- että muut ärsykkeet, ehdottaen että alue ei ole tiukasti kasvoselektiivinen

Socio‐cognitive, expertise‐based and appearance‐based accounts of the other‐‘race’ effect in face perception: A label‐based systematic review of neuroimaging results (advance online)

Two competing theories explain the other-‘race’ effect (ORE) either by greater perceptual expertise to same-‘race’ (SR) faces or by social categorization of other-‘race’ (OR) faces at the expense of individuation. To assess expertise and categorization contributions to the ORE, a promising—yet overlooked—approach is comparing activations for differ-ent other-‘races’. We present a label-based systematic review of neuroimaging studies reporting increased activity in response to OR faces (African, Caucasian, or Asian) when compared with the SR of participants. Hypothetically, while common activations would reflect general aspects of OR perception, ‘race’-preferential ones would represent effects of ‘race’-specific visual appearance. We find that several studies report activation of occipito-temporal and midcingu-late areas in response to faces across different other-‘races’, presumably due to high demand on the visual system and category processing. Another area reported in response to all OR faces, the caudate nucleus, suggests the involvement of socio-affective processes and behavioural regulation. Overall, our results support hybrid models—both expertise and social categorization contribute to the ORE, but they provide little evidence for reduced motivation to process OR faces. Addi-tionally, we identify areas preferentially responding to specific OR faces, reflecting effects of visual appearanc

High-gamma oscillations precede visual steady-state responses : a human electrocorticography study

The robust steady-state cortical activation elicited by flickering visual stimulation has been exploited by a wide range of scientific studies. As the fundamental neural response inherits the spectral properties of the gazed flickering, the paradigm has been used to chart cortical characteristics and their relation to pathologies. However, despite its widespread adoption, the underlying neural mechanisms are not well understood. Here, we show that the fundamental response is preceded by high-gamma (55-125 Hz) oscillations which are also synchronised to the gazed frequency. Using a subdural recording of the primary and associative visual cortices of one human subject, we demonstrate that the latencies of the high-gamma and fundamental components are highly correlated on a single-trial basis albeit that the latter is consistently delayed by approximately 55 ms. These results corroborate previous reports that top-down feedback projections are involved in the generation of the fundamental response, but, in addition, we show that trial-to-trial variability in fundamental latency is paralleled by a highly similar variability in high-gamma latency. Pathology- or paradigm-induced alterations in steady-state responses could thus originate either from deviating visual gamma responses or from aberrations in the neural feedback mechanism. Experiments designed to tease apart the two processes are expected to provide deeper insights into the studied paradigm

The anatomical substrates of feature integration during object processing.

Objects can be identified from a number of perceptual attributes, including visual, auditory and tactile sensory input. The integration of these perceptual attributes constitutes our semantic knowledge of an object representation. This research uses functional neuroimaging to investigate the brain areas that integrate perceptual features into an object representation, and how these regions are modulated by stimulus- and task-specific features. A series of experiments are reported that utilise different types of perceptual integration, both within and across sensory modalities. These include 1) the integration of visual form with colour, 2) the integration of visual and auditory object features, and 3) the integration of visual and tactile abstract shapes. Across these experiments I have also manipulated additional factors, including the meaning of the perceptual information (meaningful objects versus meaningless shapes), the verbal or non-verbal nature of the perceptual inputs (e.g. spoken words versus environmental sounds) and the congruency of crossmodal inputs. These experiments have identified a network of brain regions both common to, and selective for, different types of object feature integration. For instance, I have identified a common bilateral network involved in the integration and association of crossmodal audiovisual objects and intra-modal auditory or visual object pairs. However, I have also determined that activation in response to the same concepts can be modulated by the type of stimulus input (verbal versus nonverbal), the timing of those inputs (simultaneous versus sequential presentation), and the congruency of stimulus pairs (congruent versus incongruent). Taken together, the results from these experiments demonstrate modulations of neuronal activation by different object attributes at multiple different levels of the object processing hierarchy, from early sensory processing through to stored object representations. Critically, these differential effects have even been observed with the same conceptual stimuli. Together these findings highlight the need for a model of object feature processing that can account for the functional demands that elicit these anatomical differences

Holistic and Analytic Representations' of Ignored and Attended Objects

Attended images prime both themselves and their left-right reflections, whereas ignored images prime themselves but not their reflections (Stankiewicz, Hummel, & Cooper, 1998). These and other effects are predicted by the hybrid theory of object recognition (Hummel & Stankiewicz, 1996a) that the human visual system represents ignored images holistically (i.e., view-based), and attended images both holistically and analytically (i.e., part-based). In nine experiments using a naming task the predictions of the model were tested with split, plane-rotated and depth-rotated views of common objects. Consistent with the prediction of the hybrid theory, Experiments 1 and 3 demonstrated that split images primed their intact and split counterparts when they were attended but not when they were ignored, whereas intact images primed themselves whether they were attended or not. Experiment 2 demonstrated that a substantial component of the observed priming for attended split images was specifically visual. In Experiment 5, attended images primed themselves and their plane-rotated versions (90°) whereas ignored images only primed themselves but not their rotated versions. Experiment 6 tested whether rotated objects with a definite upright orientation prime themselves in the same view. Substantial priming was observed for attended and ignored objects when shown in their upright view. However, rotated objects with a definite upright orientation primed themselves only when attended but not when ignored. This result indicates that ignored images make contact with stored representations. Experiment 7 replicated the findings of Stankiewicz et al. for mirror images but with grey-level rendered 3D images. Experiment 8 tested priming for these objects using orientations in which parts change from study to test view. As before, there was substantial priming in all but the ignored-rotated condition. However, there was a greater reduction in priming for attended rotated objects than for ignored rotated objects. This result indicates that the representations mediating recognition of attended images are specifically sensitive to part changes. In Experiment 9, objects were rotated in depth such that equivalent parts were visible in both views. As in Experiment 7, the priming effects of view and attention were additive. These data provide strong evidence that one function of visual attention is to permit the generation of analytic (i.e., part-based) representations of object shape. At the same time these results show that object recognition is also mediated by additional holistic representations