Pupillary response to auditory versus visual mental loading: a pilot study using super 8-mm photography.

Summary.-The present investigation was two-fold in purpose: to test the hypothesis that auditory mental loading would require greater mental effort and larger resultant pupillary dilation than visual mental loading, and to provide evidence for the feasibility of super 8-mm photography for pupillometric research. Subjects were 30 college students. Stimuli to be stored in memory and repeated aloud in reverse order were seven-digit number series. Series were either presented visually from 35-mm slides or auditorily from a taped recording. Pupillary responses were recorded with a super 8-mm movie camera. Pupil diameter was measured to the nearest centimeter on a projected image. Results did not support the hypothesis, but methodulogically strong evidence supported 8-mm photography for pupillometry research. Studies relating pupil size to mental effort are quite numerous (Hess, 1972). Kahneman and Beatty (1966) employed a digit-span task which required subjects listened to a digit series, stored it in memory (mental loading), then repeated it aloud (mental unloading). . Pupil size increased regularly during loading and grew smaller during unloading until returning to baseline. Maximum dilation occurred just prior to responding. A study by Gardner, Beltramo, and Krinsky (1975) which dealt with immediate versus delayed recall showed pupillary constriction occurred with active rehearsal during the retention interval. Research on auditory stimuli and mental loading has been reported (Janisse, 1974) but no studies have differentially analyzed auditory versus visual stimulation. The present pilot study was designed in part to test the hypothesis that auditory loading would require greater menti1 effort and larger dilation. Historically, pupillometric technology has relied upon either 16-mm photography or television pupillometers (Hakerem, 1967). The standard for 16-mm apparatus was originated by Hess, who detailed a description of his equipment (1972). Many manufacturers sell television pupillometers (Hess, 1972; Young & Sheena, 1975). The cost of either apparatus mode is prohibitive. The author has developed a modified Hesstype apparatus adapted for super 8-mm photography which was far less expensive to build. The second purpose of this study was to provide evidence for the feasibility of 8-mm photographic equipment for pupillometric research. Subjects were 30 undergraduate and graduate students who volunteered. There were 17 males and 13 females. Only subjects with 20/20 uncorrected vision were tested to avoid unwanted reflections from corrective lenses. The apparatus was a modified Hess-type pupillometer (Hess, 1972). The box was 45-cm by 45-cm by 76-cm with a padded viewing aperture at the front and a 30.5-cm by 30.5-cm rear-projection screen at the back. An adjustable chin rest was used to keep the subject's head stationary. The subject's left eye was photographed with a Chinon XL555 super 8-mm movie camera in the macrozoom mode at f/8, using Kodak Type G ASA 160 color film. The camera was directly in front of the subject but below the sagittal plane. It was mounted at an angle of 45". Illumination in the box was provided by two 25-W bulbs mounted on either side of the box 7-cm from the front and 5-cm from