Just by briefly looking at a face, we can identify a widerange of information about a person. We are able to access invariantinformation – such as age, sex and ethnicity. As well as changeable information- such as emotion. Although the ease of which we are able to do this makes theprocess seem uncomplicated, Face perception is arguably the most advancedvisual ability that we possess.
The extensive research that has been conductedon this skill has shown that face perception is dependent on preferentialresponse to faces of the network of neural mechanisms (Duchaine & Yovel, 2015). It is long standing knowledge that face selective cells havebeen found present in monkey’s inferior temporal (IT) cortex (Gross, 2005). In morerecent research using fMRI studies, it has also been found that faceselectivity is present in the same regions of the brain within monkeys (Tsao, Freiwald, Knutsen,Mandeville & Tootell, 2003.; Tsao, Freiwald, Tootell & Livingstone,2006) and Marmosets (Hung,Yen, Ciuchta, Papoti, Bock, Leopold & Silva, 2015) However, findingsfrom these studies are not always consistent and require further research toestablish a solid relationship between these domains. In Humans however, thereare multiple regions that are responsible for the perception of faces.
Haxbyand colleagues (2000) neural model, has been influential in guiding theresearch of face processing. They theorised that there was a rift between thecore system that is responsible in the way that we process the visualappearance of faces– made up of the Occipital Face Area (OFA), the FusiformFace Area (FFA), and the posterior Superior Temporal Sulcus (pSTS)- and a morecomplex, extensive system that derives the socially relevant information fromfaces, such as emotions (Viscontidi Oleggio Castello, Halchenko, Guntupalli, Gors & Gobbini, 2017).The FFA itself has been at the centre of a debate, modularists theorise thatthe FFA is specifically responsive to faces (Kanwisher & Yovel, 2009), while generalistschallenge that assumption and believe that FFA is an expert of a wide range ofvisual categories, including faces but it is not specifically responsive tothem (Gauthier et al.,2003). Beyond that is Haxby and colleagues assumption that facialperception is taken out by a much more complex network that is beyond FFAexclusively. This essay will aim to support Haxby et al.’s (2000) model, and focus solely onthis core system and will integrate the use offunctional-Magnetic-Resonance-Imaging (fMRI) andTranscranial-Magnetic-Stimulation (TMS) as proof for this system, as well asbringing in some research from functional-Magnetic-Resonance-Angiography (fMR-A)studies. These will be used to evaluate the core system that is involved inface perception.
Eachtechnique PARAGRAPH ON FMRI AND TMS FFA In the modelproposed by Haxby et al. (2000), the FFA is mainly responsible for processinginformation such as facial identity, but is much less involved in processingthings such as facial expression, which are aspects that are changeable. Fromthe time when the model was introduced, this has been an area of great interestto researchers, and has received a great deal of support from fMR-A studies.These studies have been able to establish the degree to which therepresentation of facial identity is view specific, or view invariant. Theyhave compared the FFA’s response to two same-identity/same-view faces to twosame-identity/different-view faces. They found a higher response to thesame-identity/different-view faces, which indicated that these faces arecharacterised as different in the FFA, leading researchers to conclude that therepresentation of identity is view-specifc. (Davies-Thompson,Gouws & Andrews 2009; Ewbank & Andrews, 2008; Xu & Biederman, 2010;Duchaine & Yovel, 2015).
Kanwisher et al. (1997) found reliable fMRI activation of FFAin over 80% of their participants, the FFA favoured faces over a range ofassorted objects such as cutlery, cars and animals. Pruce et al (1996) found similar resultsusing fMRI techiques, finding that facial stimuli caused a significant amountof right hemispheric activation, with characteristic patterns localised to theFFA in comparison to when the participants were shown letter strings.
Thesestudies both support Haxby et al.’s (2000) first FFA predication that FFA is extremelyattuned to face stimuli and lead researchers to label the FFA as the faceprocessor. Anotherprediction of FFA is that it is selectively receptive to a range of invariantfacial information such as identity. Tong et al. (2000) with fMRI studies, discoveredthat the FFA responded equally as strong to cartoon and human faces, as well asshowing an equal reaction to front and profile views but a very minoractivation for non-facial stimuli. This too supports the second prediction ofHaxby et al (2000). There arealso claims that the FFA is involved in expression processing (Bernstein & Yovel 2015).Ganel, Valyear,Goshen-Gottstein & Goodale (2005) found that the FFA responds verystrongly to facial expression when it is both attended and unattended andfollowing this, its response is influenced by how intense the facial expressionis.
fMR-A studies similarly found that the FFA is attuned to variations infacial expressions across faces (Xu & Biederman, 2010). Furthermore, when studying a patient who suffered brain damage whichresulted in the destruction of the right FFA, but no damage to the right OFA orright pSTS who had poor expression recognition, it was suggested that the FFAmust contribute to expression recognition for static faces at the very least (Dalrymple et al. 2011).With this being said, it is indicated that the FFA and the pSTS are responsiblefor expression processing, however they may extract different types ofinformation from an expression.
Said, Haxby & Todorov (2011) presented participants with computer generated faces, these facesdiffered from average faces in different ways. In one condition the facesvaried in expression, in the other they varied in face shape regarding typicalface shape, but not in expression. The FFA was found to show a reaction todeviations from the average face in both conditions, where the pSTS was onlysensitive to those that differed in expression. Suggesting that the response ofthe FFA could reflect a broad sensitivity to shape information, where the pSTSmay only be responsive to facial stimuli that give emotional information. OFA The functionsthat the Occipital Face Area carries out are complimentary to that ofFFA. Haxby et al.
(2000) theorise that it processes invariant information priorto FFA processing it, and focuses specifically on facial features. These claimswere tested by Pitcher etal. (2009) who used TMS studies to substantiate this. Using stimuliconsisting of faces, bodies and novel objects, they demonstrated a tripledissociation in OFA using perceptual discrimination tasks that involved stimuliconsisting of faces, bodies as well as novel objects. Alongside the OFA theytested the extrastriate body area (EBA) and the Lateral Occipital complex(LOC).
Firstly they used fMRI to confine the appropriate locations with theregion of interest (RoI). RoI allows regions of the brain to be studiedobjectively without an individual’s anatomical differences having an effect (Kanwisher & Yovel, 2009). Hereafter the TMS was applied and delivereddiscerning effects, where OFA disruption did influence the participant’sdecisions on facial stimuli, it did not affect the participant’s decisions onany of the other stimuli types. EBA was found to influence perception on bodiesand LOC influenced perception of novel objects, disruptions to these areas alsodid not show any effect on participant’s decisions of other stimulus types. Showingthat there must be distributed modality, the discerning processing of differentperceptual categories must take place in distinct regions and thereforesupporting the Haxby et al. (2000) model. PSTS The third keyprediction of Haxby et al’s (2000) model is that STS reacts to the unpredictableand changeable characteristics of faces, such as gaze movement, facialexpression and movement of the mouth.
fMRI and TMS studies have been used inorder to corroborate the claims of Haxby et al.’s (2000) model. A group whohave been of high interest in this area are individuals with Autistic SpectrumDisorder (ASD). This is due to the association with abnormal gaze and emotionperception (Golarai et al.2006). Pelphrey etal. (2005) discovered, when using an event related fMRI, that inindividuals with ASD, STS was not prone to intention violation, as were thecontrol group. In the study an actors gaze would differ when a new objectentered the scene, the gaze would be moved to the expected – the object, or theunexpected- an open space.
Both groups equally noticed the change in gaze, butSTS activation differed significantly between them. It was also found that STSwas more active when the individual was attending more to gaze than facialidentity, this proposes the uniqueness from FFA. TMS has alsobeen used to localise and disrupt STS. Grossman et al. (2005) delivered a 10-minutesuccession of repetitive low frequency stimulations to individuals.
They weredelivered at 1Hz as this is used to produce lengthier effects than if it wasdelivered at 10Hz. When placed over the right posterior STS these stimulations compromisedbiological motion perception, this was measured by point light animations. Thisobservation shows the STS’s fundamental role in understanding dynamicinformation, which is extremely important following facial perception. Alternativeto these views, some speculate that STS is activated from any generic stimulithat transmits intention, not just face-specific stimuli, as it was shown thatSTS was activated when basic geometric shapes transmitted intention (Golarai et al., 2006). Contraryto this, other research done using fMRI indicated that STS is receptive to bothmoving and motionless eyes, as well as mouths, but did not respond to movingshapes (Puce et al.,1998).
Nevertheless, both ofthese perspectives suggest that STS activation is imperative in reacting tosignals that are important to prospective behaviours that occur after facialperception. Prosopagnosiais a type of visual agnosia that is specific to faces, however it is very rarethat an individual just has prosopagnosia, it is extremely common for them tohave other recognition deficits along side it (Kanwisher, 2000). Anatomicaldifferences between patients have made it extremely difficult to generaliseinformation in support or opposition of claims made in regards to thecondition, however TMS has made in possible for researchers to recreate theeffects in healthy patients to demonstrate modularity within the faceperception network. The lack of redundancy within the FFA, OFA and pSTS havebeen theorized to diminish the capability for reorganisation amongst the intactregions, and therefore damage to any individual region can be more disastrous(DeGutis, Chiu, Grosso & Cohan, 2014). fMRI studies have shown that the FFAis responsive to both face configuration as well as parts of the face, whereasOFA and pSTS are responsive to the parts of the face, but not the correctconfiguration of these (Liuet al.
, 2010). Studies have shown the functional autonomy that ispresent in the face processing network. Barton (2008) discovered that patients who hadlesions to their right occipital-temporal regions had much more specificdiscrepancies when perceiving facial structure and configuration, inparticularly the eye area, while those who had anterior temporal damage hadmuch more difficulty in accessing memories of faces. CONCLUSIONThere are many studies that back up the claims of Haxby etal’s (2000) model and exhibit the dissociation amid the mechanisms of thesystem. In particularly, Hoffman& Haxby (2000) used fMRI and repetition-detection tasks, firstlyparticipants were instructed whether they were required to concentrate on theidentity of the face, or the direction of the gaze. Identity was predominantlyrelated to FFA and OFA, whereas gaze was linked with STS. By using this blockdesign, they determined invariant and changeable processing systems, one thatprocesses identity, and the other that processes expression and gaze, which isconsistent with the forecasts of Haxby et al’s (2000) model.
In Summary, there is a wealth of evidence from fMRI, TMS and fMR-A studiesto support three apparent regions that are involved in the perception of faces,in turn supporting the Haxby et al. (2000) model. FFA is extremely responsiveto the generic facial stimuli and it also processes identity holistically,additionally it is thought to be related to face memory (Kanwisher & Yovel, 2009; Golorai etal., 2006). OFAis an area that is much more responsive to facial features (Pitcher at al., 2009)and STS is receptive to the unpredictable and changeable information that aface can give us (Goloraiet al.
, 2006). Although theseregions are all extremely valuable and important in the perception of faces,Haxby et al. (2000) clarified that face perception is also reliant on externalprocesses. Using fMRI studies, Rossion et al. (2012) discovered multiple regions that areinvolved in the process that go beyond the core system, these regions werediscovered by using multi-dimensional stimuli. They concluded that connectivitybetween systems is just as important as modular functioning in the perceptionof faces, and Haxby et al. (2000) proposed a link between and within the coreand extended networks. Haxby et al.
(2010) supported this view by proposing a further discrepancybetween maximal and significant activation within the facial perceptionnetwork. The FFA, OFA and STS maximally react to invariant and changeableinformation respectively, but extended systems, for example the amygdala are proposedto respond significantly to this information. Haxby et al (2010) suggested thatthis is because they are more vulnerable to the more generic traits thatstimuli possess. This discrepancy is valuable in supporting the idea ofdistributed-modularity. Turati(2004) proposed that this allows general expertise effects to besupportable as non-facial stimuli may actually resemble a face in generic ways.
For example the front of a building may comprise of symmetry similar to that ofa face, in turn activating FFA. In disagreement to this claim Kanwisher & Yovel (2009)found that facial stimuli reliably activated FFA compared to non-facialstimuli.An interesting claim was made by Tsao & Livingstone (2008), they proposed that all visualstimuli have the same issues. These issues are image changes regardingposition, illumination and occlusion.
Futhermore, Turati (2004) suggested that faces are unique andspecial because they have noticeable perceptual configuration, they proposedthat this is due to us innately having non-specific perceptual boundaries.