The retinae in the principal eyes of the Adanson jumping spiders have four distinct photosensitive layers. When an image is in focus on one layer of the spider’s retina, it is out of focus on the other layers. Although you might think this would make their vision blurry, the spiders actually use the extent to which the second image is out of focus to determine the distance they are from objects. Nagata et al. (2012) showed that the spider’s eyes focus a sharp image on the first layer of the retina, leaving blurred images on the subsequent layers. The spider then compares the sharpness of the first image to the blurriness of subsequent images to compute an estimate of depth. Thus, these spiders use information from different layers of each retina to compute depth. This fascinating way of determining depth is quite different from how our visual system determines depth.
Use this activity to see how the relative blurriness of the different retinal layers is related depth.
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