Our visual system evolved in a natural environment, and is reasonable to assume that it has been sculpted to be better at recognizing a definite ecological relevant set of objects. Face perception is an essential feat that conveys to us information about identity, gender, and mood which is useful in social and emotional interactions. It has been recently suggested that humans and macaques share most of the cortical face processing machinery. In this vein, the general purpose of this project is to dissect the neural mechanisms participating in detection of multiple features of face stimuli, and test if the system plays a role during conscious and unconscious visibility of faces. The conceptual and methodological framework supporting this general purpose is grounded on a novel experimental platform consisting in coupling fMRI to functionally map face-selective cortical patches and multielectrode/stimulation techniques to record specific cell properties within each patch and test for causal relationships in macaque monkeys.
The first aim will pursue to characterize tuning specialization and directionality of information flow across face patches. Emergence of selectivity will be examined analyzing preferred and anti-preferred face spaces to investigate if local cortical inhibition plays a role. Once this first step is achieved, interference techniques to measure neural responses to artificial stimulation and to natural visual stimulation will be used. The second set of experiments will evaluate the correlation and causal link between neural signals (single unit and LFP) and behavioral responses in a detection task. Once the system model has been initially characterized, the final part of this project will determine the neural signature of conscious and unconscious face recognition. Perceptual visibility manipulations will be achieved using an object-substitution masking, a widely used psychopysical paradigm in humans that permit a systematic control of the perceived stimulus. I hypothesize that visual information can reach early nodes of the patch system in a feedforward fashion, building up selectivity even at near-threshold visual stimuli presentations, and that this mode can be dissociated from perceptual awareness, which requires feedback mechanisms. These interrelated approaches using the face patch system as a specialized model for visual object recognition enhances the probability of revealing novel information of the inner workings mediating visual object perception.
We daily recognize our conspecifics without any effort and in many contexts and this ability allows us to infer emotional states that ultimately guide our immediate behavior. Our ability to perform this stresses the importance of understanding the inner workings of face processing. This project is centered on gaining knowledge on the neural mechanisms that mediate face visibility and eventually object recognition as a whole. The research proposal is distinguished because it employs a combination of methodological approaches intended to disentangle the biological implementations of face recognition as an ecological relevant object category in a recently well defined brain network.