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Hi Luis The pupil doesn't just constrict to an increase in overall light level, it also constricts if there's a change in the visual input in pretty much any way - any local light increases (even if there are equal local light decreases), change in spatial frequency composition, motion, colour... My guess would be that the faster the speed, the more the visual input is changing from moment-to-moment, and so the stronger the effect of these reflexes. I'd expect quite extreme effects with natural visual input (assuming that's what you're using), given that they are likely to be high contrast, coloured, moving, etc. I've been doing experiments with static, low contrast, monochrome visual input, and still get pupillary constrictions on stimulus onset which are large enough to counteract even quite moderate task-induced dilations. Hope this helps. Gillian --On 09 December 2003 12:09 +0100 Luis Nunes <[log in to unmask]> wrote: > Dear colleagues > > In several experiments carried on with participants that drove an > instrumented vehicle in open roads we have found systematically a pupil > size increment effect attributable to increased mental workload - > (independent from variations attributable to daylight changes) - and this > effect has also been consistent with subjective effort measures. We have > also found, congruently, momentary pupill size peaks corresponding to > particularly demanding traffic situations like emergency braking, etc. > > But in recent experiments focused on speed effects on visual behaviour, > we found a pupil size reduction attributable to driving speed, but we > have no explanation for this. The reanalysis of data prior experiments > regarding speed seems to confirm this effect also. > > Has anyone found this effect, or has anyone some idea about a possible > explanation ? > > Thanks > > > Luis Miguel Nunes > Dirección General de Tráfico > c/Josefa Valcárcel 28 > 28027-Madrid > > Tel. +34 91 301 82 38 > > -- > EYE-MOVEMENT mailing list ([log in to unmask]) > N.B. Replies are sent to the list, not the sender > To unsubscribe, etc. see > http://www.jiscmail.ac.uk/files/eye-movement/introduction.html Other > queries to list owner at [log in to unmask] > ---------------------- G Porter, Experimental Psychology [log in to unmask] -- EYE-MOVEMENT mailing list ([log in to unmask]) N.B. Replies are sent to the list, not the sender To unsubscribe, etc. see http://www.jiscmail.ac.uk/files/eye-movement/introduction.html Other queries to list owner at [log in to unmask]