Transfer of Conditioned Fear Potentiated Startle across Equivalence Classes. an Exploratory Study
Conditioned fear, as well as conditioned avoidance, is a key element for behavioral accounts of anxiety and its disorders (Barlow, 2002) In fear conditioning, a neutral stimulus (CS) acquires the capacity to elicit fear (and related emotional reactions) after being repeatedly paired with an aversive unconditioned stimulus (UCS) However, for many instances of human fear in daily life it may be difficult to find an instance of aversive conditioning that accounts for the observed current fear (King, Gullone, Ollendick, 1998, Menzies Clarke, 1993a,b) Fear generalization to situations other than the original aversive event appears as a key process for the explanation of these instances. Watson and Rayner's (1920) famous little Albert case constitutes the canonical example of fear generalization: after fear conditioning to a white rat, a toddler (little Albert) showed fear reactions to diverse furry things, none of which had been directly paired with aversive stimulation. This example illustrates the more traditional view of generalization as a form of transfer along a continuum of perceptual similarity amongst the directly conditioned stimulus and the generalization stimuli. This type of generalization of fear in humans is being researched with renovated interest in recent times (e.g. Dunsmoor LaBar, 2013, Lissek, Biggs, Rabin, et al, 2008; Lissek, Powers, McClure, et al. 2014; van Meurs, Wiggert, Wicker, Lissek, 2014).Generalization can also take place on the basis of features other than physical similarity (Dymond, Dunsmoor, Vervliet, Roche, Hermans, 2015) Increasing evidence shows that fear reactions transfer according to conceptual/semantic categories. For instance, Dunsmoor, White, and LaBar (2011) found that fear generalized more easily between conceptually related stimuli (e.g. spider and web) than between conceptually unrelated stimuli (e.g. spider and hospital corridor) Research on this form of conceptual/ semantic transfer has the disadvantage of poor experimental control over the learning histories that might have resulted in the formation of the semantic categories to which the stimuli belong. For instance, words like web and spider must have been directly paired on uncountable occasions during the learner's lifetime, which renders conceptual/ semantic generalization findings amenable to explanation in terms of higher order or sensory preconditioning (see Declerq De Houwer, 2009).Beyond semantic relatedness, a limited but growing empirical evidence shows that fear generalization also occurs between stimuli belonging to the same de novo created category (e.g. Dougher, Augustson, Markham, Greenway, Wulfert, 1994; Luciano, Valdivia Salas, Ruiz, et al, 2013; Rodriguez Valverde, Luciano, BamesHolmes, 2009; Vervoort, Vervliet, Bennett, Baeyens, 2014) that is, a set of physically dissimilar stimuli that are grouped arbitrarily upon some form of training. This type of work has been conducted in the field of behavior analysis under the labels stimulus equivalence and transfer of functions (Dougher Markham, 1996; Hayes, Gifford, Wilson, 1996; Sidman, 1994) (more recently this phenomenon has also been researched under the umbrella term symbolic generalization; see Dymond, Dunsmoor, Vervliet, Roche, Hermans, 2015).Stimulus equivalence emerges readily in language able humans after traimng interrelated conditional discriminations among arbitrary (physically dissimilar) stimuli. Typically, conditional discriminations are trained and tested with matching to sample (MTS) procedures: for instance, when choosing Bl in the presence of A1 is reinforced (Al Bl) and choosing Cl in the presence of A1 is also reinforced (Al Cl) untrained relations of symmetry (choosing Al in the presence of either Bl or Cl: Bl Al and Cl Al) and transitivity (choosing Cl in the presence of Bl, and vice versa: Bl Cl and Cl Bl) will appear in the absence of feedback.