Avoidance reaction

Abstract: Numerous studies use arm movements (arm flexion and extension) to investigate the interaction between emotional stimuli and approach/avoidance behaviour. In many experiments, however, these arm movements are ambiguous. Arm flexion can be interpreted either as pulling (approach) or as withdrawing (avoidance). On the contrary, arm extension can be interpreted as reaching (approach) or as pushing (avoidance). This ambiguity can be resolved by regarding approach and avoidance as flexible action plans that are represented in terms of their effects. Approach actions reduce the distance between a stimulus and the self, whereas avoidance actions increase that distance. In this view, action effects are an integral part of the representation of an action. As a result, a neutral action can become an approach or avoidance reaction if it repeatedly results in decreasing or increasing the distance to a valenced stimulus. This hypothesis was tested in the current study. Participants responded to positive and negative words using key-presses. These "neutral" responses (not involving arm flexion or extension) were consistently followed by a stimulus movement toward or away from the participant. Responses to emotional words were faster when the response's effect was congruent with stimulus valence, suggesting that approach/avoidance actions are indeed defined in terms of their outcomes.

Abstract: Unilateral mechanical stimulation of a uropod elicited an avoidance reaction in the crayfish Procambarus clarkii. Depending upon the animal's size, either one of two alternative behavioral acts emerged as the avoidance reaction to similar stimuli. A stationary resting posture of the crayfish and a passive extension of the abdomen were prerequisite conditions for inducing the avoidance reaction. In small animals (less than 10 cm in body length), the "dart" response was mainly elicited. Animals responded with a sudden closing of both uropods and rapid forward walking to scuttle away from the stimulus source. This act was regarded as one form of escape behavior. With increasing animal size, the "turn" response became more probable than the "dart" response. During the "turn" response, the uropod on the stimulated side opened and that on the contralateral side closed. This act was frequently followed by a rapid turning movement towards the stimulus source with an extension or flexion of the abdomen. This act was also regarded as a variant form of defensive behavior. In large animals with autotomized chelipeds, the response to the uropod stimulation reverted to that of the "dart" response after 2 to 3 days.