The larger number of trials and the expanded sample size also allowed us to conduct an exploratory analysis of neural correlates of the cognitive overload state. In deviation from the original protocol, we significantly increased the number of trials and expanded the sample size to increase the signal-to-noise ratio.
Psychopy perceptual load serial#
Using the simple span task with a serial auditory presentation, we were able to monitor WM loading at a single-item level. We aimed to determine whether at the end of the retention interval after the presentation of the 13th digit, pupil size would remain at the peak level or return to baseline. In the current study, we replicated the original Peavler's ( 1974) experiment presenting participants with sequences of 5, 9, or 13 digits. Given the association between pupil size and arousal, the exact shape of this pattern is indicative of how people respond to cognitive (over-)load: while an inverted U-shaped pattern would imply that cognitive and physiological effort are released, a prolonged plateau would imply that they are maintained even when task demands exceed the capacity limit. By contrast, other studies have found a simpler, bi-phasic pattern whereby pupil size increases with load and reaches a stable plateau at the capacity limit (Cabestrero et al., 2009 Peavler, 1974). Several studies have found an inverted U-shaped pattern where increasing memory load up to the capacity limit is associated with increasing pupil dilation, while further memory overload is associated with pupil constriction (Granholm et al., 1996 Johnson et al., 2014 Poock, 1973). How exactly does the pupil respond to cognitive overload? Two conflicting patterns of results have emerged over the years (Figure 1). However, the majority used modest set sizes (4–6 items), while only a few studies used set sizes that exceeded the memory capacity, leading to cognitive overload.
Most previous pupillometric studies of cognitive load, employing the digit span task, showed a linear relationship between the number of presented memory items and pupil size (Karatekin, 2004 Klingner et al., 2011 Piquado et al., 2010). For example, maintaining information in working memory (WM) is accompanied by subjectively noticeable cognitive effort, and an increase in memory set size and cognitive effort is associated with pupil dilation during WM tasks (Heitz et al., 2008 Kahneman & Beatty, 1966 Karatekin et al., 2004 Klingner et al., 2011 Unsworth & Robison, 2015). The human pupil dilates during effortful cognitive activities such as those that require increasing deployed attentional control resources (Chen & Epps, 2014 Kursawe & Zimmer, 2015 Laeng et al., 2011 Lisi et al., 2015 Marquart & de Winter, 2015 Meghanathan et al., 2014). These results suggest that associating alpha with the focus of attention and distractor suppression is not warranted. Although memory capacity limits were exceeded and effort was released (as indicated by pupil dilation), alpha continued to decrease with increasing memory load.
Based on the described above triphasic pattern of pupil size temporal dynamics, we concluded that cognitive overload causes physiological systems to reset, and release effort. Both theta activity and pupil size, after the initial rise, expressed a pattern of a short plateau and a decrease with reaching the state of memory overload, indicating that pupil size and theta possibly have similar neural mechanisms.
Psychopy perceptual load trial#
Each trial consisted of sequences of either 5, 9, or 13 digits, each separated by 2 s. Eighty-six participants were presented with a digit span task involving the serial auditory presentation of items. The objective of the current study was to characterize the central and autonomic nervous system changes associated with memory overload, by means of combined recording of electroencephalogram (EEG) and pupillometry. It is unclear, however, how the nervous system responds to a working memory load exceeding typical capacity limits. Most previous psychophysiological studies manipulated verbal working memory load in a narrow range (an average load of 5 items). Understanding the physiological correlates of cognitive overload has implications for gauging the limits of human cognition, developing novel methods to define cognitive overload, and mitigating the negative outcomes associated with overload.
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