The findings of the studies presented in the current thesis provide some support for the ‘criterion setting’ version of the current hypothesis (see Section 1.4.1). Under this account, experience with our movements furnishes models with distinct criteria for identifying internal states – for instance, a fast walker’s criterion for identifying anger will be faster than a slow walker’s criterion, as suggested by the findings in Chapters 2 and 3. Such a criterion setting account could also explain the findings in Chapter 6. For example, a typical individual tends to move with lower jerk than autistic individuals. Therefore, an animation demonstrating seducing – which is conveyed through low jerk,
145 smooth movements – may not be identified as such when a typical individual is
interpreting an autistic action because the jerk is too high to be categorised this way.
An alternative to the criterion setting account is that experience with one’s own actions results in ‘perceptual narrowing’ of action models, such that we are most sensitive to kinematic information that aligns with one’s own action kinematics. Chapter 5 found no evidence to support such a hypothesis given that autistic and typical individuals
exhibited no ‘own-group’ perceptual enhancement, which also makes this interpretation of the results of Chapter 6 less likely.
However, as outlined in Chapter 1 (see Section 1.2.3) there are several action perception studies that do demonstrate enhanced perceptual sensitivity for actions specific to one’s own motoric repertoire. One important distinction between these previous action perception studies and the studies presented in the current thesis are the type of actions and perceptual judgments measured. For example, in the previous studies participants are often asked to predict the outcomes of another’s action sequence (Aglioti et al., 2008; Brault, et al., 2012; Diersch, et al., 2012; Diersch et al., 2013; Kandel, et al., 2000; Sebanz & Shiffrar, 2009) or distinguish self-action from that of others (Knoblich & Prinz, 2001; Loula et al., 2005) using movement stimuli that are highly practiced by the participants. As mentioned in Chapter 1, the sensitivity account likely requires exclusive, extensive and highly repetitive experience with a rigid action in order to finely tune action models. An expert will, by definition, have the necessary rigid motoric experiences to develop highly precise models of action sequences that enable very accurate predictions about others movements that fall within their specific motoric expertise. In contrast a novice, despite possibly having the perceptual capabilities to detect kinematic information within others’ actions, might not have any model of the observed action sequence by which to assess the kinematic information which they
146 perceive. The perceptual sensitivity effects observed in these previous studies could be due to fine-tuning of kinematic models which only occurs following highly specific action experiences. The kinematic features of an individual’s actions as measured in the studies presented in this thesis – e.g., high velocity or high jerk actions – are generalised features that are perhaps not akin to the restrained action sequences experienced by professional athletes.
Moreover, it is possible that an initial step, before fine-tuning of one’s action models occurs, is a criterion setting process. For example, one might initially learn coarse mappings between kinematic cues and goals (in the case of experts, learning the predicted action sequence and outcome) or internal states, and hence furnish action models with specific kinematic criteria that represent different outcomes or internal states, before models are refined and become more precise following extensive and rigid rehearsal. ‘Perceptual narrowing’ or this secondary fine-tuning may be unlikely to occur with respect to the vast range of internal states we experience in our varied everyday lives. For example, when we feel sad there will be some continuity between our
experiences (e.g., decrease in velocity from typical pace), but this might vary depending on the context (e.g., whether we are at home or at work) and we will also perform a range of actions depending on what we are doing (e.g., walking to catch a bus or
cooking). Therefore our models of our internal states might not be as precise as specific action sequences that we perform repetitively in order to produce actions with expert precision, and thus internal state attribution may rely more on a criterion setting type mechanism.
It is possible, however, that ‘perceptual narrowing’ for specific internal states occurs following intensive experience conveying that given state. For example, individuals who experience clinical depression will frequently move much slower than average,
147 while concurrently experiencing feelings of sadness (Michalak et al., 2009). These individuals may have criteria for different internal states, which are centred around their action experiences, but also become highly sensitive to variations in sad (or slow) kinematic signals. Subsequently, these depressed individuals may be able to distinguish very accurately subtle differences in others’ slow (sad) movements, but fail to recognise similar subtleties in faster movements, and therefore cannot differentiate their
interaction partner’s bliss from jubilation. On the other hand, an individual who frequently experiences aggression and moves very quickly may be astute at reading differing levels of anger in others, but fail to recognise varying levels of sadness (or fear). Future work could look to further address the relationship between ‘perceptual narrowing’ and internal state experiences by studying groups of individuals who have more extreme internal state experiences (e.g., individuals with clinical depression or antisocial personality disorder) and measuring their different internal state criteria (which are predicted to follow a similar pattern as that presented in the current thesis based on their typical action kinematics) as well as perceptual sensitivity to variations in different internal state cues (which are predicted to show greatest sensitivity for internal states they frequently experience).
8.4. The role of executive processes in using models of action to interpret others’