Mantis Experiments

32 Zeki S. The representation of colours in the cerebral cortex. In all experiments, individual mantises were fitted with blue and green colored filters to enable the display of 3D stimuli to them. These were tear-drop shaped glasses cut out of filters which had been distributed with a preprint of a previously published paper [] and had a maximum length of 7 cm. In order to fit the glasses on, the mantises were temporarily immobilized by placing their cages in a freezer (Argos Value Range DD1-05 Tabletop Freezer) for 5-8 min. The mantises were subsequently held down with Plasticine and the glasses were fitted with beeswax and rosin onto the front of the mantis. Once the glasses were fixed, the mantis was released and placed back in its cage. The mantises were allowed to recover overnight and experiments were conducted after this.

33 Kleiner M.

Brainard D.

Pelli D. What’s new in Psychtoolbox-3?. 17 Nityananda V.

Tarawneh G.

Rosner R.

Nicolas J.

Crichton S.

Read J. Insect stereopsis demonstrated using a 3D insect cinema. All stimuli were displayed on a DELL U2413 LED monitor (1920 × 1200 pixels; 51.8 × 32.4 cm; 60 Hz refresh rate). All stimuli were custom written in MATLAB (Mathworks) with the Psychophysics Toolbox []. The mantis was placed on a stand 10 cm away from the screen. All mantises were tested for motivation with a 3D stimulus before and after experiments. This stimulus consisted of a disc swirling in from the periphery to the center of the screen in front of the mantis. The stimulus had crossed disparity across the two eyes and simulated a target of 1 cm diameter, 2.5 cm in front of the mantis. This stimulus has previously been shown to be attractive to mantises and elicit strikes []. Experiments were only carried out if the mantis struck at this stimulus twice in a row and the data were used if the mantis did the same after the experiment. Across all experimental conditions five out of 131 experimental runs were excluded because mantises did not strike after the trials were conducted. All our stimuli used this size and motion of target, and a “trial” is defined as one presentation of this spiral motion ( Figure 1 B). In all experiments, we left a 60 s pause between trials to avoid habituation to the stimuli. One experimental run consisted of a set of trials presented one after the other in the same session. Depending on the experiment, mantises were presented 20-36 trials per experimental run.

17 Nityananda V.

Tarawneh G.

Rosner R.

Nicolas J.

Crichton S.

Read J. Insect stereopsis demonstrated using a 3D insect cinema. 17 Nityananda V.

Tarawneh G.

Rosner R.

Nicolas J.

Crichton S.

Read J. Insect stereopsis demonstrated using a 3D insect cinema. o when directly in front of the mantis; see [ 34 Nityananda V.

Tarawneh G.

Errington S.

Serrano-Pedraza I.

Read J. The optomotor response of the praying mantis is driven predominantly by the central visual field. In all experiments, we used a background stimulus consisting of a cyan background covered in dots ( Figure 1 A). Since the mantis was viewing the background through the green and blue glasses, the cyan background was visible in both eyes and was adjusted to have equal luminance in both eyes, taking account of the mantis spectral sensitivity function []. Furthermore, 50% of the dots in each channel (blue or green) had the minimum luminance of zero and the other 50% had the maximum luminance (see [] for details of the max/min luminance in each channel). This would correspond to ‘black’ and ‘white’ dots against a ‘gray’ background in the appropriate channel. For one set of experiments, we used small dots with a diameter of 25 pixels (corresponding to 1.8° based on the average angle subtended by a pixel across different screen locations, and to 3.9when directly in front of the mantis; see [] for a discussion of this difference) and a density of 55 dots in every 100 by 100 pixel square. For the other set of experiments, the background dots consisted of large dots with a diameter of 60 pixels (corresponding to 4.4° / 9.4°) and a density of 3 dots in every 100 by 100 pixel square. All experiments were conducted at an ambient temperature of 20-25°C.

Correlation Experiments 23 Nityananda V.

Bissianna G.

Tarawneh G.

Read J. Small or far away? Size and distance perception in the praying mantis. 17 Nityananda V.

Tarawneh G.

Rosner R.

Nicolas J.

Crichton S.

Read J. Insect stereopsis demonstrated using a 3D insect cinema. 23 Nityananda V.

Bissianna G.

Tarawneh G.

Read J. Small or far away? Size and distance perception in the praying mantis. In these experiments, the background consisted of a stationary random dot pattern. The target was a patch of the same pattern, moving coherently over the background (occluding it where it passed). In the correlated condition, the target and background had disparities of opposite sign, so that the target appeared in the crossed condition as a disk moving over a patterned surface, and in the uncrossed condition as a circular hole cut in the surface. During experiments, interleaved trials were run with the disparity of the target patch being crossed, zero or uncrossed in different trials. The disparity in the crossed condition was chosen so as to simulate a target 2.5 cm from the mantis (i.e., 7.5 cm from the screen), which is an attractive distance for the mantis to strike at a target []. In the uncrossed condition, the value of the screen parallax was the same as in the crossed condition but the positions of the target in the two eyes were reversed. In the zero disparity condition, both eyes saw the patch at the same location (i.e., on the screen, 10 cm away from the mantis). The target patch in all conditions spiraled in over five seconds from the periphery of the screen to stop in front of the mantis where it moved with small jerky motions for another two seconds. Further details of the target motion are available in previously published studies []. We tested mantises (n = 20 for the large dots; n = 17 for the small dots) with these stimuli in two separate experiments. In the first experiment, two correlation conditions were interleaved. In the first condition, both background and target dots were correlated, i.e., white dots in one eye corresponded to white dots in a matching position in the other eye and black dots corresponded to black dots. In the second condition, the dots were anti-correlated, i.e., white dots in one eye corresponded to black dots in a matching position in the other and vice versa. In each experimental run, five trials were run for each of the three disparities in each of these two conditions for a total of 30 trials. This experimental run was carried out twice on each animal, making for a total of ten replicate trials for every combination of disparity and correlation condition and thus a total of 60 trials per mantis. Trials with different combinations of disparity and correlation-type were randomly interleaved through the experiments. A new background was rendered after every trial. In the second experiment, both background and target dots were uncorrelated, i.e., the position and luminance of dots in one eye did not correspond to any matching position or luminance in the other eye. The disparity in these stimuli was defined purely by the position of the moving target. Mantises (n = 7) were presented with ten replicate trials for each disparity in this experiment, with each experiment thus having thirty trials. A new background was rendered after every trial.

Matched Motion Experiments To ask whether mantis stereo relied on matching motion direction in both eyes, we defined targets with motion in either the same or different directions in each eye. To avoid depth cues associated with interocular velocity differences, we used vertical motion to define our target regions. The background consisted of uncorrelated small or large dots as described above. A focal target region was defined in each eye with the distance between the centers of these regions equal to the disparity defined screen parallax as in the experiment above. Within these regions, dots continuously moved with either upward or downward motion with a speed of 120 pixels per second. The moving dots vanished when they reached the edge of the region and new dots continuously replaced them from the opposite edge. These motion-defined regions spiraled into the center with the motion as defined in the previous experiments. In four separate conditions, the dots moved upward in both eyes (Up-Up), downward in both eyes (Down-Down), upward in on eye and downward in the other (Up-Down) or the reverse (Down-Up). Each of these conditions were presented with the position of the regions in the eyes being crossed or uncrossed. An experimental run consisted of six replicates each for each of the two disparity conditions for the Up-Up and Down-Down conditions and three replicates each for each of the two disparity conditions for the Up-Down and Down-Up conditions. The lower number of replicates in the latter case reflected our assumption that, while the direction of motion might be important (i.e., Up-Up might be different from Down-Down), eye of presentation would not matter in the mismatched motion condition (i.e., Up-Down would elicit the same response as Down-Up). Each of six mantises were presented with two such experimental runs with all conditions interleaved resulting in a total of 72 trials per mantis. The Up-Up and Down-Down conditions had 12 replicates of each disparity condition and the Up-Down and Down-Up conditions had 6 replicates each for each disparity condition.