Tactile guidance of prey capture in Etruscan shrews

Abstract

Whereas visuomotor behaviors and visual object recognition have been studied in detail, we know relatively little about tactile object representations. We investigate a new model system for the tactile guidance of behavior, namely prey (cricket) capture by one of the smallest mammals, the Etruscan shrew, Suncus etruscus. Because of their high metabolic rate and nocturnal lifestyle, Etruscan shrews are forced to detect, overwhelm, and kill prey in large numbers in darkness. Crickets are exquisitely mechanosensitive, fast-moving prey, almost as big as the shrew itself. Shrews succeed in hunting by lateralized, precise, and fast attacks. Removal experiments demonstrate that both macrovibrissae and microvibrissae are required for prey capture, with the macrovibrissae being involved in attack targeting. Experiments with artificial prey replica show that tactile shape cues are both necessary and sufficient for evoking attacks. Prey representations are motion-and sizeinvariant. Shrews distinguish and memorize prey features. Corrective maneuvers and cricket shape manipulation experiments indicate that shrew behavior is guided by Gestalt-like prey descriptions. Thus, tactile object recognition in Etruscan shrews shares characteristics of human visual object recognition, but it proceeds faster and occurs in a 20,000-times-smaller brain.active touch ͉ barrel cortex ͉ object recognition ͉ Suncus etruscus ͉ whisker

Biomimetic tactile target acquisition, tracking and capture

“…The only bottom-up features extracted are essentially 'shapelets' (oriented fragments of surface [29]) and therefore the approach promises general discrimination in a mobile condition with any sufficiently-rich whisker geometry. This technique is inspired by the apparent use of a gestalt-like approach by hunting shrews [12] but also likely reflects a more general approach to perception in biological systems [31]. Whilst the model we have developed assumes contact occurs at the tip of the whisker, the extension to contact along the shaft is straightforward provided the contact location can be estimated, and this certainly appears to be possible [44,45].…”

“…When the shrew commences a strike on its prey, a particular location (the thorax) is targeted in the great majority of cases. Based on several lines of reasoning, but in particular the ability of the shrew to accurately target an area of the prey that has not yet been directly sensed, a gestalt-like representation of the prey has been inferred [12]. In any case, the relative sizes of the prey and the whisker field indicate that only part of the prey can be sensed at any one time ( Figure 1, left).…”

“…Finally, the strategy of measuring motion (including the value of the parameter v moving ) to orient the prey model and, thus, identify the 'strike point' was chosen as a consequence of Preybot's radial symmetry, and is not a requirement of this approach to control. Shrews will make accurate attacks on stationary crickets and attacks seem to be targeted, rather, through recognition of body parts [12]. A future investigation might select and orient the model of the prey by feature recognition, rather than by motion measurement.…”

“…This animal must capture prey-sometimes not much smaller than the shrew itself ( Figure 1, left)-in twilight or dark conditions [11]. To that end, it relies on large facial 'whiskers' (macrovibrissae), common to many mammals ( Figure 1, middle), for both identification and localisation [12]. Whisker-triggered attacks on prey are highly spatially selective and may target an area that has not yet fallen within the whisker sensory field, indicating that they use a 'gestalt-like' representation of the prey, functionally perceiving the whole prey despite sensing just part of it [12].…”

“…To that end, it relies on large facial 'whiskers' (macrovibrissae), common to many mammals ( Figure 1, middle), for both identification and localisation [12]. Whisker-triggered attacks on prey are highly spatially selective and may target an area that has not yet fallen within the whisker sensory field, indicating that they use a 'gestalt-like' representation of the prey, functionally perceiving the whole prey despite sensing just part of it [12]. Overall, this behaviour looks enviable to any roboticist, and we are therefore motivated to understand what is involved in its reproduction.…”