Startle responses

The responses of chicks startled near the end of a bout of feeding or preening were different from, and measurably greater than, those of chicks startled at the beginning of bouts of these activities. This result provides evidence about changes in motivational state during a bout of activity. It is proposed that causal factors, which are changing during the bout, may initiate an attentional change as the point of transition to another activity approaches. Distractibility and information-processing rate may be increased near the end of an activity because the individual can then attend to a greater variety of inputs than it could earlier in the bout. This would maximise the efficiency of the ensuing behavioural change. In order to carry out these experiments, bouts of feeding and preening were measured using a criterion based on log survivor curves for inter-event gap-lengths. The effects on the response of the time during a bout at which interruption occurs, were shown by chicks of ...

The cognitive and emotional modulation of the cardiac defense response was investigated in this study. One hundred forty-four participants were exposed to three presentations of an intense auditory stimulus while performing one of four attentional tasks: a control task, an external perceptual tracking task, and two internal tasks presented at either easy or difficult memory loads. State anxiety was also manipulated by requiring each group to perform either with or without the threat of shock. Heart rate and vasomotor activity were recorded. Results indicated that only the externally directed tracking task led to potentiation of the cardiac response. No predicted effects for attentional demands were obtained and the anxiety manipulation did not appear to have an effect. Differences between measures were also observed, particularly with respect to response habituation. Unlike cardiac activity, vasomotor responses displayed resistance to habituation. The results are discussed in relation to contemporary accounts of defensive responding.