Spider eye movement

The principal and AL eyes may also work together to gather visual information. A recent study (Jakob et al., 2018) investigated how lateral eyes direct the principal eyes of jumping spiders when tracking objects. In order to test this,Phidippus audax spiders were tethered in front of an eyetracker that recorded the gaze direction of the principal eyes. Visual stimuli of different shapes and movement speeds were presented before and after masking the ALEs with removable paint. When unmasked spiders were shown a moving disk, the principal eye retinas moved close together and were able to track it. Meanwhile, spiders with their AL eyes masked were unable to track moving objects, with their principal eye retinas remaining further apart and reacting only briefly when the objects crossed their field of view. However, when the spiders were presented with a motionless object that appeared in the center of the principal eye’s field of view, they actively scanned it regardless of whether the secondary eyes were masked or unmasked. This indicates that masking the secondary eyes does not prevent the principal eyes from investigating stationary objects, but they are needed for targeting stimuli outside of the principal eye’s field of view (Jakob et al., 2018). The integration between principal and secondary eyes has also been studied in Cupiennius salei (Family Ctenidae). The principal eyes of ctenids are moveable, but they are controlled by four muscles instead of six as in jumping spiders (Kaps, 1996) (Land, 1969). Thus, they are not able to engage in complex movements such as torsion. When spiders had their principal eyes masked, they maintained the same eye muscle activity, but masking the secondary eyes reduced principal eye movement (Neuhofer et al., 2009). The researchers concluded that the secondary eyes of C. salei are involved in movement detection, while the principal eyes require input from the secondary eyes to move normally.