Effort during visual search and counting: Insights from pupillometry

Abstract

We investigated the processing effort during visual search and counting tasks using a pupil dilation measure. Search difficulty was manipulated by varying the number of distractors as well as the heterogeneity of the distractors. More difficult visual search resulted in more pupil dilation than did less difficult search. These results confirm a link between effort and increased pupil dilation. The pupil dilated more during the counting task than during target-absent search, even though the displays were identical, and the two tasks were matched for reaction time. The moment-to-moment dilation pattern during search suggests little effort in the early stages, but increasingly more effort towards response, whereas the counting task involved an increased initial effort, which was sustained throughout the trial. These patterns can be interpreted in terms of the differential memory load for item locations in each task. In an additional experiment, increasing the spatial memory requirements of the search evoked a corresponding increase in pupil dilation. These results support the view that search tasks involve some, but limited, memory for item locations, and the effort associated with this memory load increases during the trials. In contrast, counting involves a heavy locational memory component from the start.

Your Effort Is Showing! Pupil Dilation Reveals Memory Heuristics

“…It has long been known that, when people perform challenging tasks that require more cognitive effort, their pupils dilate (Porter, Troscianko, & Gilchrist, 2007), possibly representing a summed index of brain activity associated with such tasks (Beatty & Kahneman, 1966). Beatty (1982) summarized the attractive qualities of the pupil reflex that made it Kahneman"s (1973) primary index of mental processing load in his theory of attention allocation.…”

“…Variations in luminance across stimuli, sudden onsets of stimuli, and variations in color can all induce pupillary responses (Porter et al, 2007), necessitating tight experimental control. Porter and Troscianko (2003) discussed several methodological approaches that can minimize unwanted pupil reflexes.…”

Safe and sensible baseline correction of pupil-size data

“…Gamlin et al, 2007), and variations of subtractive baseline correction (Binda, Pereverzeva, & Murray, 2013;Hupé, Lamirel, & Lorenceau, 2009;Jainta, Vernet, Yang, & Kapoula, 2011;Knapen et al, 2016;Koelewijn, Zekveld, Festen, & Kramer, 2012;e.g. Laeng & Sulutvedt, 2014;Murphy, Moort, & Nieuwenhuis, 2016;Porter, Troscianko, & Gilchrist, 2007;Privitera, Renninger, Carney, Klein, & Aguilar, 2010) seem somewhat more common than variations of divisive baseline correction (Bonmati-Carrion et al, 2016;Herbst, Sander, Milea, LundAndersen, & Kawasaki, 2011;Mathôt, van der Linden, Grainger, & Vitu, 2013;H. Wilhelm, Lüdtke, & Wilhelm, 1998).…”

The pupillometric precision of a remote video eye tracker

“…In contrast, remote eye trackers, which usually devote fewer pixels to each pupil and must correct for variations in the camerapupil distance, exhibit worse precision. However, there are some applications which require remote, free-head eye tracking or pupillometry, such as studies with infants [Chatham et al 2009] or investigations of small changes in anxiety, distraction, or mental effort [Porter et al 2007]. Quantifying the accompanying loss of precision is important, both to guide equipment choices and to determine the number of participants and trials required to measure a given magnitude pupillary response using a remote eye tracker.…”