selective attention
1.2.1 Darwin’s legacy
This theoretical tradition originated after Charles Darwin’s seminal work on emotional expression (Darwin, 1872). By comparing the emotional facial expressions of humans and animals throughout the world, Darwin proposed that the configural patterns of facial muscles expressing emotions were due to a “principle of serviceable associated habits” (Darwin, 1872, p. 34). According to this principle, universal emotional expressions did not evolve for the sole purpose of communicating, but rather as an incidental product due to particular actions associated with strong emotions.
According to him, prototypical facial expressions find their origins in the phylogeny of the species, and would be the remainder of particular actions that led to evolutionary advantages for the species. The purpose of the facial expression of disgust, for instance, would be to expel from the mouth a piece of food appraised as dangerous for the organism (see also Rozin & Fallon, 1987;
Wiens et al., 2008), and the purpose of the facial expression of fear would be to gather as much sensory information as possible (see also Susskind et al., 2008).
Tomkins (1962), Ekman (1992, 1999, 2004), Izard (1992, 2007) and others, extended Darwin’s work, and formalised a full theoretical account on emotional systems. Primarily, these views posit a finite number of basic emotions, which emerged in response to evolutionary pressure. These discrete entities possess unique properties, distinguishing one from the others, and are believed to be mediated by separate and distinct brain substrates (Ekman, 2003; Izard, 2007). A basic emotion occurs rapidly, and automatically, upon perception and classification of a stimulus as belonging to specific classes of events.
The classes of these events are of upmost importance, as some results emphasise the universality of the themes representing these events across cultures (Boucher & Brant, 1981; Matsumoto et al., 1988; Scherer et al., 1983). Ekman (2004, p. 125) refers to these automatic appraising mechanisms as “autoappraisers [...] scanning continuously, out of our conscious awareness, watching out for the themes and variations of the events that have been relevant to our survival.” To ensure an adaptive function to the processes in the daily life, supporting the acquisition of new information, for instance, he further proposes that autoappraisers query and update some kind of an “emotional
alert database” (2004, p. 125), collecting information about goals and direct concerns for the individual.
Proponents of the basic emotion theories argued for a long time about the number of such basic emotions, varying from six to over ten. A consensus seems to have been reached however, in the form of a list of six emotions: anger, disgust, fear, joy/happiness, sadness and surprise (Ekman, 2003; Izard, 2007). These six emotions are considered fundamental, as they can be combined and blended into more complex emotions (e.g., shame or guilt).
By setting the emphasis on the adaptive role of emotions in dealing with key survival issues, basic emotion theorists argue that emotional systems evolved concurrently, providing individuals with better ways of handling their environment. Amongst which is the quick selective attention to elements of the environment carrying some relevance for the individual’s survival, in preparation for an appropriate response.
1.2.2 The “fear module” hypothesis: Attention will preferentially be drawn by fear-related stimuli
In this context, fear is often presented as the most important emotion. Not only does it explicitly refer to objects of major value for survival, it has a special importance in our modern society due to the prevalence of anxiety disorders (for a review, see Bishop, 2007). In an early work, Seligman (1970, 1971) showed that certain threatening stimuli (e.g., snakes, spiders) were more susceptible to fearful conditioning than other types of stimuli. To explain his results, he formulated the pre-paredness hypothesis, according to which this ease of associability would be due to the threatening contexts encountered throughout the evolution of the species, rather than to individual features of the stimuli. In other words, evolutionary pressure would have favoured the associative mechanisms that would provide individuals with the ability to easily recognise threatening situations.
Influenced by Fodor’s modular approach (1983), ¨Ohman and colleagues extended this work and developed the concept of the fear module ( ¨Ohman & Mineka, 2001; Mineka & ¨Ohman, 2002): a particular module dedicated to the detection of fear-related situations (Figure 1.2). This selectivity to the sole class of threatening events is justified by the need for minimal neural processing to capture attention, and to promote rapid defencive response ( ¨Ohman & Wiens, 2004). The ease of associability through conditioning described by Seligman would thus ensure that the range of stimuli that activates the fear module can be expanded to specific, new threatening stimuli of the
Figure 1.2: The fear module ( ¨Ohman & Wiens, 2004). Upon perception of a fear-related stimulus, the fear module activates a cascade of events meant to prepare the individual for immediate, appropriate response.
environment ( ¨Ohman et al., 1975, 1976). This particular module would not require any conscious recognition of the perceived stimulus. It is also proposed to be encapsulated, that is independent from other modules. Once activated, it would behave in a ballistic fashion, relatively impenetrable to higher-order influences. Finally, it would be centred around the amygdala. This brain structure is indeed in a very good place in the perceptual processing stream for this task (LeDoux, 1996).
According to this hypothesis, anxiety disorders and phobias can be explained by both the natural inclination of our species towards a specific class of threatening events (Seligman, 1970, 1971;
Ohman & Mineka, 2001), and the particular malfunction of the processes involved in the detection¨ of threatening stimuli, or the learning of fearful reactions (Mineka & ¨Ohman, 2002; Juth et al., 2005). The formal object of this module was originally proposed to be restricted to any stimulus of the environment that has been experienced through a phylogenetic contingency with physical harm (e.g., reptile predators, aggressive social encounters). This claim has later been refined to include ontogenetic threat stimuli as well (Brosch & Sharma, 2005; Blanchette, 2006; Flykt et al., 2007).
In this framework, the experienced contingencies between threat and harm is believed to have resulted in hardwired connections in the brain, located in the amygdala, supporting reflexive-like behaviours (automatic, fast, pre-attentive and preconscious) promoting the survival of the individual.
A general prediction can thus be made: any threatening stimulus will yield to an orienting reflex in preparation for an immediate response (Mogg & Bradley, 1998, 1999). This prediction is supported by a growing amount of data pointing at an advantage for detecting threatening stimuli (e.g., Flykt et al., 2007; Brosch & Sharma, 2005). In a series of experiments using the visual search paradigm, for instance, ¨Ohman and colleagues showed that participants were faster at detecting a schematic
face expressing anger within a board of smiling faces, than at detecting a smiling face within a board of angry faces ( ¨Ohman et al., 2001). They later demonstrated that this effect was enhanced in socially anxious participants (Juth et al., 2005). They report, however, that when they used pictures of faces in place of schematic faces, healthy participants were faster and more accurate at detecting happy faces than angry faces. They explain this effect by arguing that schematic faces were more controlled (e.g., in terms of intensity and expressiveness) compared to the schematic pictures they used. Results to a memory task comparing both types of stimuli indeed suggest that the pictures of smiling faces were more easily processed and recognised than schematic faces (Juth et al., 2005).
The scope of the fear module is explicitly restricted to threatening stimuli, and does not account for the perception or response to stimuli belonging to other classes of emotions. An implicit corollary to this hypothesis would be that there exist similar dedicated processing systems for the other so-called basic emotions, as described by Ekman (2003), or Izard (2007). Given the evolutionary value for survival of threatening stimuli, it is expected that modules concerned with positive stimuli would yield to less prominent orienting reflexes than the fear module.