Orientation by Jumping Spiders in the Absence of Visual Feedback

ABSTRACT Jumping spiders turn to face moving objects. These turns are mediated by the lateral eyes. They can be accomplished accurately whether or not the spider sees the relative movement of the stimulus across the retinae which would normally result from such a turn. The spider’s response to an adequate stimulus may be: (i) to make a ‘complete’ turn resulting in fixation by the antero-median eyes; (ii) to make a ‘partial’ turn of 10–20°, whose magnitude is independent of stimulus position, and which does not result in fixation, or (iii) to ignore it. To be seen, a stimulus must subtend more than 0–7° (slightly less than the distance between receptors) and must move through a minimum angle of about i°. The probability of a turn being made is greatest for stimuli 40–90° from the spider’s front, and decreases to a low value for stimuli behind the animal, and immediately in front of it. Repeated presentation of a stimulus to one part of the retina results in a rapid decrease to zero of the probability of a turn being made, but turns can still be evoked by moving the stimulus a few degrees to a previously unstimulated part of the retina. Habituation does not affect the sizes of the few turns that are made. Dishabituation can be caused by mechanical stimulation, or it may occur spontaneously. The fields of view of the lateral eyes have been measured in the horizontal plane by blinding each eye and determining the parts of the visual field from which turns could not be evoked. Three kinds of response mediated by the lateral eyes, in addition to turns towards the stimulus, are described.