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Introduction Pupillometric measures of cognitive and emotional processes

Introduction Pupillometric measures of cognitive and emotional processes Changes in pupil diameter provide a unique window on brain activity. We would like to thank Dr John Andreassi, editor of the International Journal of Psychophysiology, for the opportunity to be guest editors of this special issue on pupillometric studies. This volume is an expansion of the symposium 'Pupillometry and Cognition in Schizo-phrenia' presented at the 11th World Congress of Psychophysiology held in Montreal in 2002, chaired by the first author. A number of additional contributions have been included that survey much of the current state of research involving cognitive and emotional processes, and the relevance of pupillary mechanisms to the elucidation of neuro-psychiatric problems. All of the papers were peer-reviewed in accord with Journal standards, and we would like to acknowledge and thank all of the reviewers and authors for their contributions. Pupillometric methods are used to measure variations in the diameter of the pupillary aperture of the eye in response to psychophysical andyor psychological stimuli. In keeping with the focus of International Journal of Psychophysiology, this special issue emphasizes pupillometric measures of psychological processes, rather than psychophysi-cal processes, despite the wealth of research on the latter. Pupillary responses can be used to index the extent of central nervous system processing allocated to a task. The extent of pupil dilation evoked by a task reflects activation in processing modules of the brain, regardless of whether those modules contribute information processing (e.g. attentional allocation; stimulus identification; working memory maintenance; semantic elaboration; response organization; motor output) or emotional processing (e.g. attach or interpret an affective valence). In numerous studies of normal individuals, pupil size has been found to increase in response to increased processing demands. For example, pupil size recorded during a digit span recall task systematically increases following the presentation of each additional to-be-recalled digit and then returns to resting baseline size after the digits are recalled. Increased pupil dilation is also found when the number of multiplicands is increased on mental arithmetic tasks, the syntactic complexity of sentences is increased on sentence comprehension tasks, the difficulty of perceptual discriminations is increased, and when processing pleasant and unpleasant stimuli relative to neutral stimuli. As such, pupillometry can be broadly applied in psychological research to inform normal and abnormal cognitive and emotional functioning. One goal of this special issue is to stimulate the application of pupillometric methods in psychophysiological research. For over two …