Shifting attention: assessing antennular ‘gaze’ in the hermit crab Pagurus bernhardus

Attention (focused information gathering) is crucial for many cognitive processes. Traditionally dichotomized as reflexive or voluntary, attention is often assessed using vision, in behavioural research. However, invertebrate information acquisition often utilizes chemosensation or mechanosensation, potentially limiting the efficacy of a vision-based approach. We examined attention in Pagurus bernhardus hermit crabs, using antennules (the crustacean first antennae) as indicators of attentional shifts. Considering a change in flicking direction as analogous to a shift in gaze, we examined if hermit crabs show evidence of reflexive or voluntary attention. We exposed crabs to a chemosensory stimulus while manipulating factors influencing vulnerability (i.e. shell presence and lighting conditions). We aimed to examine how vulnerability influences attention by modifying signal salience (the value of the information contained in a stimulus) and individual vigilance (the ability to monitor environmental changes). Given that attention varies with stimulus importance and individual condition, we predicted that antennule shift likelihood, latency and duration would vary by stimulus type and both intrinsic (shell presence) and extrinsic (light regime) vulnerability. We found that attention can be assessed by monitoring the antennular ‘gaze’ or direction of antennule pointing. Crab vulnerability altered patterns of reflexive attention, modifying patterns of signal salience and individual vigilance. Vulnerability also affected attention duration, demonstrating that hermit crabs may adjust attention based on context, indicative of voluntary attention. This study highlights the utility of a novel approach to assessing attention in invertebrates, especially those reliant on chemosensory cues for behavioural decisions and cognitive processes essential to species' fitness. • We monitored antennular (chemosensory) ‘gaze’ to assess attention in hermit crabs. • We examined if and how vulnerability alters attention, salience and vigilance. • Hermit crabs demonstrated reflexive and voluntary attention. • Crab vulnerability alters salience, vigilance and overall patterns of attention. • Antennular movement can be used to study attention, analogous to gaze in eyes.