Psychophysical investigation of vigilance decrement in jumping spiders: overstimulation or understimulation?

The inability to maintain signal detection performance with time on task, or vigilance decrement, is widely studied in people because of its profound implications on attention-demanding tasks over sustained periods of time (e.g., air-traffic control). According to the resource depletion (overload) theory, a faster decrement is expected in tasks that are cognitively demanding or overstimulating, while the underload theory predicts steeper decrements in tasks that provide too little cognitive load, or understimulation. Using Trite planiceps, a jumping spider which is an active visual hunter, we investigated vigilance decrement to repetitive visual stimuli. Spiders were tethered in front of two stimulus presentation monitors and were given a polystyrene ball to hold. Movement of this ball indicates an attempt to turn towards a visual stimulus presented to a pair of laterally facing (anterior lateral) eyes for closer investigation with high acuity forward-facing (anterior median) eyes. Vigilance decrement is easily measured, as moving visual stimuli trigger clear optokinetic responses. We manipulated task difficulty by varying the contrast of the stimulus and the degree of 'noise' displayed on the screen over which the stimulus moved, thus affecting the signal:noise ratio. Additionally, we manipulated motivation by paired testing of hungry and sated spiders. All factors affected the vigilance decrement, but the key variable affecting decrement was stimulus contrast. Spiders exhibited a steeper decrement in the harder tasks, aligning with the resource depletion theory.

Caffeine affects the vigilance decrement of Trite planiceps jumping spiders (Salticidae).

In jumping spiders (Salticidae), the vigilance decrement, or decrease in response to a repeated visual stimulus over time, directly parallels that found in humans. Explanations for the vigilance decrement in the human literature are heavily mentalistic and central nervous system (CNS) based, whereas response decrements in invertebrates are typically thought of as habituation at the sensory periphery. Here we explored whether the salticid vigilance decrement could be CNS modulated by using caffeine, which is a well-known CNS stimulant for both vertebrates and invertebrates. We used paired tests in which Trite planiceps Simon spiders were randomly given a drop of either caffeinated water or distilled water and were then shown dot stimuli presented on monitors. We measured both general "walking," or activity, as a control for physical fatigue, and optomotor responses to the stimuli. We found that the vigilance decrement was significantly shallower (i.e., spiders were more responsive for longer) when spiders were administered caffeine compared with water; furthermore, these spiders were also generally more active throughout the testing period and thus were not physically impaired. Our results suggest that, in at least some invertebrates, CNS modulation of the vigilance decrement is likely. (PsycINFO Database Record (c) 2019 APA, all rights reserved).