Neuroimaging and the intentional stance

One of the greatest strengths of neuroimaging approaches such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) is its potential to covertly examine mental processes without the confound of explicit probes for self-report. There have been a handful of studies that have examined the neural correlates of intentionality cues, using animations like those created by Heider and Simmel (1944). Castelli and colleagues (2000) presented three types of animations while collecting PET scans, shapes that moved: (1) randomly; (2) in a goal-directed way; and (3) in ways that implied complex mental states (such as deception). In half the cases, participants were told what sort of animation they would see (the cued condition), and the order of these blocks was counterbalanced. For half the participants then, the uncued condition followed the cued, allowing for the possibility that awareness of the animation-types biased their attention and inferences during the former condition. This may explain why no differences were found during cued and uncued animations, prompting the researchers to combine the data across conditions for analysis.

Animations meant to elicit theory-of-mind attributions elicited more activation in several areas relative to the random animations: (1) the bilateral temporal parietal junction (TPJ); in the posterior superior temporal sulcus (STS); (2) bilateral basal temporal regions, including the temporal poles; (3) the bilateral extrastriate cortex: and (4) the medial prefrontal cortex (MPFC). A follow-up study involving both autistic patients and normally developing controls replicated this finding, and also found that autistics had less activation in the basal temporal area, the STS and TPJ, and the MPFC (Castelli et al 2002). Behavioural data have shown that those with autism are less likely to report percepts of intentionality when viewing these types of stimuli, allowing for the inference that these brain areas are responsible for engaging the intentional stance (Abell et al 2000, Castelli et al 2002). Corroborating this supposition, the TPJ and STS, temporal poles and MPFC have all been implicated in mentalising processes in numerous studies, using a variety of methods and tasks (Gallagher & Frith 2003).

Blakemore and colleagues (2003) performed an influential fMRI study that employed simple shape animations to parse perceptions of animacy and contingency, as well as examine the effect of drawing attention to the contingency relations (via an explicit probe). Different parts of the brain were associated with viewing animate compared to contingent stimuli, and when both qualities were present activation was observed in superior parietal areas. Notably, when participants were cued to attend to the contingent movements, activation was observed in the right middle frontal gyrus (MFG) and left STS. It is worth noting that the stimuli in this study were much less complex than those in the previous studies, and did not involve imbuing shapes with complicated mental states.

Similar areas of activation were found in a study by Shultz and colleagues (2004), who presented animations of one circle chasing another. In half the animations, the chasing circle predicted the end-state of the other circle in order to catch it, and in the other half this circle merely followed the other. When comparing the predicting condition to the following condition, activations were observed around the STS in both hemispheres. In conjunction, similar to the findings of Blakemore and colleagues (2003), explicitly drawing attention to the 'strategy' of the circle was associated with the left STS. The STS and TPJ have proven very important for the discussion of basic cues for intentionality; a number of researchers have argued that the STS is implicated in the understanding of biological motion, specifically with respect to intentions and goals (e.g. Allison et al 2000, Pelphrey et al 2004a, Saxe et al 2004).

One question that arises from the work reviewed thus far is whether the STS also codes for featural cues that trigger the intentional stance, along with motion cues. There is some evidence for this. Activation in the STS has been observed for static images of features that cue intentionality, such as eyes, mouths, hands and faces; in some cases, however, these static images may have implied motion (for a review see Allison et al 2000). Because activations in this area are observed both when abstract shapes and realistic portrayals of biological agents are used as stimuli, it has been conjectured that the STS codes for intentional movement regardless of form (Shultz et al 2004). Direct comparisons of cartoon and realistic motion, however, are methodologically difficult to achieve. Pelphrey and colleagues (2003) found that the STS did not appear to respond differentially to the movements of a computer-animated person compared to a similarly rendered 'robot' constructed of cylinders and spheres. In contrast, a separate fMRI study found that although the STS responded to very abstract representations of biological motion (point-light displays), it demonstrated a slightly stronger response to videos of real people in motion (Beauchamp et al 2003). A PET study, involving observations of grasping actions by a real hand compared to a 3D virtual reality hand, found the right TPJ near the posterior STS was more activated by the real hand; the right temporal pole also showed a similar preference (Perani et al 2001).

In a recent study (Mar et al 2006), we examined whether the brain responds differently to complex dynamic videos of social interactions presented in either a cartoon or realistic fashion. Footage for the film Waking Life (Linklater 2001) was shot using real actors, and later transformed by computer animators into a cartoon. Motion kinematics from the real footage were thus preserved in the animated version, and although both versions had numerous cues for animacy and inten-tionality (e.g. self-propelled movement, faces and other biological features) one was obviously realistic while the other was a cartoon (see Fig. 1). Equivalent content was shown in both versions, and shots within scenes alternated between cartoon and real. Participants were not prompted to make any social judgement,

FIG. 1. Screenshot from the video stimuli employed by Mar et al (2006); cartoon version above real version.

but only instructed to watch the videos closely, which were presented without sound. We found that the right STS and TPJ were more activated while participants watched realistic scenes compared to cartoon scenes (see Fig. 2A). Even though the cartoon version was closely matched to the real version, the latter appears to have preferentially engaged brain areas known to be involved in mentalizing and the inference of intentions from behaviour.

Interestingly, the right MFG was also more activated during the real condition (see Fig. 2B), and others have found similar activations to be associated with attending to contingency relations in the presence of animacy (Blakemore et al 2003), making judgements regarding persons (Mason et al 2004) and inferences of intentionality when perceiving actions (Pelphrey et al 2004a). Moreover, because this study did not employ explicit prompts for social judgement, this appears to be evidence for the spontaneous triggering of the intentional stance based upon perceptual cues (cf. German et al 2004). The right STS, TPJ and MFG thus appear to be highly sensitive to subtle cues signalling intentionality, moving beyond

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FIG. 2. Activation in the right STS, TPJ (A) and MFG (B) for the Real > Cartoon contrast from Mar et al (2006). Activations superimposed on an average of all T1-weighted structural scans for participants. Legend indicates t-value.

FIG. 2. Activation in the right STS, TPJ (A) and MFG (B) for the Real > Cartoon contrast from Mar et al (2006). Activations superimposed on an average of all T1-weighted structural scans for participants. Legend indicates t-value.

animate motion and biological features (present in both versions of the stimuli) to the perception of targets as belonging to the real world. Previous work has also demonstrated such sensitivity to subtle cues of intentionality in the STS, such as a preference for mutual gaze as opposed to averted gaze from a dynamic computer-animated person (Pelphrey et al 2004b). It appears that activation in the STS and TPJ may be modulated by the number of cues present that signal intentionality. While basic motion cues (e.g. animated shapes) as well as static featural cues (e.g. faces and eyes) can result in engagement of these superior lateral temporal regions, combining these cues appears to result in greater activity.

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