Comparative Evidence For Associative Learning In Task Switching

Comparative Evidence For Associative Learning In Task Switching Christina Meier (CM374@exeter.ac.uk) Stephen E. G. Lea (S.E.G.Lea@exeter.ac.uk) Charlotte L. D. Forrest (CLF206@exeter.ac.uk) Katharina Angerer (KA288@exeter.ac.uk) Ian P. L. McLaren (I.P.L.McLaren@exeter.ac.uk) Department of Psychology, Washington Singer Laboratories Exeter, EX4 4QG, UK Abstract Humans can perform several different tasks on the same set of stimuli in rapid alternation. Each task, signaled by a distinct task cue, may require the classification of stimuli using a different stimulus attribute. However, such task switching performance comes at a cost, as expressed by weaker performance when switching rather than repeating tasks. This cost is often claimed to be the consequence of a mental reorientation away from the previous task and towards the new task, requiring executive control of behavior. Alternatively, task switching could simply be based on the retrieval of different cue-stimulus-response associations. In this experiment, pigeons learned go-left/go-right discriminations between grating patterns according to either their spatial frequency or their orientation, depending on the color of the pattern (the task cue). When humans solved the same tasks on the basis of verbalizable rules, they responded more slowly and made more errors on trials where they had to switch between tasks than when repeating the same task. Pigeons did not show this switch cost ; but like humans, their performance was significantly worse when the response (left or right) to a given stimulus varied between tasks than when it stayed the same (the “congruency effect”). Larger effects of both switch costs and congruency were observed in humans learning the tasks by trial and error. We discuss the potential driving factors behind these very different patterns of performance for both humans and pigeons. Keywords: executive control; associative learning; task switching; humans; pigeons; comparative cognition. Introduction Humans are able to perform two or more different tasks on the same stimulus material when cued to do so (called “task switching”). Typically, each task requires the classification of a set of stimuli according to a different stimulus attribute. The task that is to be performed in a given trial is indicated by a specific task cue (for example, subjects might be asked to judge a grating pattern by its spatial frequency when the color yellow is presented, or to classify the same stimulus according to whether it is vertically or horizontally orientated when the color red appears). However, it is still a matter of debate which cognitive mechanisms underlie human task-switching ability. Humans may classify the stimuli they see based on rules, and a common phenomenon of task switching, namely longer reaction times and higher error rates after switching tasks compared to repeating the same task (“switch costs”), has been assumed to reflect the executive control processes associated with this rule use. For example, humans might sort a series of stimuli based on their orientation while ignoring other available stimulus dimensions such as spatial frequency. In this context, switching from one task to the next involves executive control when identifying the current task, retrieving its specific stimulus-response rules into one's working memory (while deleting the rules of the previous task) and adjusting one's response reaction to the new requirements: in short, a mental disengagement from the previous task and preparation for the currently relevant task, known as task-set reconfiguration (Vandierendonck, Liefooghe & Verbruggen, 2010). Switch costs are thought to reflect the need for such reconfiguration in switch trials but not in repeat trials, for which the task-set is already available (Monsell, 2003). But, if we believe that humans have multiple processes available that support learning (McLaren, Green & Mackintosh, 1994), task-switching phenomena might be the result of associative learning mechanisms, i.e., the retrieval of cue-stimulus-response associations (Logan & Bundesen, 2003). Learning to respond correctly in a task-switching paradigm could be accomplished by associating the overall appearance of a stimulus with a certain response (Lea & Wills, 2008). Each stimulus could be categorized by using its combined dimensions and comparing its similarity to a stimulus to which the correct response is known. A task-switching phenomenon often observed in addition to switch costs, the effects of stimulus congruency (Monsell, Yeung & Azuma, 2000), might indeed be better explained by associative learning processes than task-set reconfiguration. As each task makes use of the same set of multidimensional stimuli, stimulus values on individual dimensions can be defined as either congruent or incongruent in relation to the correct response towards them. If a stimulus is congruent, it always requires the same response regardless of the current task; learning to discriminate between different congruent stimuli thus takes the form of a component discrimination, in which the correct response depends on a single element of a multidimensional stimulus. However, when an incongruent stimulus is shown, the correct response varies depending on the current task in the manner of a biconditional discrimination. Given that there is good evidence that such discriminations are difficult to learn (Harris & Livesey, 2008), it is no surprise that on trials in which a congruent stimulus is shown, reaction time and error rate are distinctly