The behavioural significance of heart rate: the Laceys' hypothesis.

The Laceys' account of the significance of heart rate changes for behaviour is critically evaluated. Two interwoven propositions are discerned in their account: first, the cardiac variations regulate central attentional activities via an afferent feedback mechanism; second, that environmental intake-rejection comprises a basic dimension underlying directional cardiac changes. Examination of pertinent psychophysiological research reveals that the first of these propositions lacks substantive support. The intra-cardiac cycle method has yielded highly equivocal results. Inter-cardiac cycle studies offer only modest correlational support and the two studies which have directly manipulated heart rate found that sensori-motor performance was largely unaffected. Difficulties also surround the other proposition. Consideration of the verbalization, pleasantness-unpleasantness and time estimation studies indicates that the relationship between heart rate and attention is variable and that heart rate is associated with factors other than attentional requirements. While the Laceys have attempted to reconcile such unfavourable evidence, conceptual clarity is frequently sacrificed in the process. It is concluded that the interpretation of cardiac responses must be sought in superordinate variables that account for both heart rate changes that can be related to attention and those that cannot, and that any afferent feedback mechanism, based on heart rate, most likely fulfills functions other than that proposed by the Laceys.