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. 2023 Aug 10;12:e81701. doi: 10.7554/eLife.81701

Figure 1. Example neuron tuned for object orientation in a gravitational reference frame.

(a, b) Stimuli demonstrating example object orientations in the full scene condition. At each object orientation, the object was positioned on the ground-like surface naturalistically by virtually immersing or ‘planting’ 15% of its mass below ground, providing physical realism for orientations that would otherwise be visibly unbalanced and ensuring that most of the object was visible at each orientation. The high-response object shape and orientation discovered in the genetic algorithm experiments was always at the center of the tested orientation range and labeled 0°. The two monkey tilt conditions are diagrammed at left. The small white dots at the center of the head (connected by vertical dashed lines) represent the virtual axis of rotation produced by a circular sled supporting the chair. Stimuli were presented on a 100°-wide display screen for 750ms (separated by 250ms blank screen intervals) while the monkey fixated a central dot. Stimuli were presented in random order for a total of 5 repetitions each. (c,d) Responses of an example IT neuron to full scene stimuli, as a function of object orientation on the screen and thus with respect to gravity, across a 100° orientation range, while the monkey was tilted –25° (c) and 25° (d). Response values are averaged across the 750ms presentation time and across 5 repetitions and smoothed with a boxcar kernel of width 50° (3 orientation values). For this neuron, object orientation tuning remained consistent with respect to gravity across the two tilt conditions, with a peak response centered at 0° (dashed vertical line). The pink triangles indicate the object orientations compared across tilts in the gravitational alignment analysis. The two leftmost values are eliminated to equate the number of comparisons with the retinal alignment analysis. (e,f) The same data plotted against orientation on the retina, corrected for 6° counter-rolling of the eyes (Figure 1—figure supplement 1). The cyan triangles indicate the response values compared across tilts in the retinal analysis. Due to 6° the shift produced by ocular counter-rolling, these comparison values were interpolated between tested screen orientations using a Catmull-Rom spline. Since for this cell orientation tuning was consistent in gravitational space, the peaks are shifted right or left by 19° each, that is 25° minus the 6° compensation for ocular counter-rotation. (g–j) Similar results were obtained for this neuron with isolated object stimuli.

Figure 1.

Figure 1—figure supplement 1. Analysis of eye counter-rotation during tilt.

Figure 1—figure supplement 1.

Eye orientation was estimated with lines connecting the center of the pupil with visualizable features at the edge of the iris. For the right and left eyes in the same monkey, the measured difference in eye orientation relative to the head was 12.65° for the right eye and 12.00° for the left eye (upper right). For the tilt experiments on all the neurons, combined across monkeys, we searched for the counterroll compensation that would produce the strongest agreement in retinal coordinates. At each compensation level tested, we normalized and summed the mean squared error (MSE) between responses at corresponding retinal positions. The best agreement in retinal coordinates (minimum MSE) was measured at 12° offset, corresponding to 6° rotation from normal in each of the tilt conditions (lower left).
Figure 1—figure supplement 2. Example neurons tuned in gravitational space and retinal space.

Figure 1—figure supplement 2.

(a, b) Stimuli demonstrating example object orientations used to study the two IT neurons. The orientation discovered in the genetic algorithm experiments is arbitrarily labeled 0°. The two monkey tilt conditions are diagrammed at left. (c, d) Responses of a gravitationally tuned IT neuron studied with the stimuli shown in (a), as a function of object orientation on the screen and thus with respect to gravity, across a 100° orientation range, while the monkey was tilted –25° (c) and 25° (d). Response values are averaged across the 750ms presentation time and across 5 repetitions and smoothed with a boxcar kernel of width 50° (3 orientation values). For this neuron, object orientation tuning remained consistent in screen/gravity space across the two tilt conditions. Other details as in Figure 1. (e, f) The same data plotted against orientation on the retina, corrected for 6° counter-rolling of the eyes in each tilt condition. Due to the shift produced by ocular counter-rolling, these comparison values were interpolated between tested screen orientations using a Catmull-Rom spline. Since orientation tuning was consistent in gravitational space, the tuning functions are shifted right or left by about 20° each. (g, h) Responses of a retinally-tuned IT neuron studied with the stimuli shown in (b), as a function of object orientation on the screen and thus with respect to gravity, across a 100° orientation range, while the monkey was tilted –25° (c) and 25° (d). In this case, the tuning peak was shifted about 40°, in the direction expected for orientation tuning in retinal space. (i,j) The same data plotted against orientation on the retina, corrected for 6° counter-rolling of the eyes in each tilt condition. The correspondence between curves in (i) and (j), with peaks at near 0°, is consistent with orientation tuning in retinal space.
Figure 1—figure supplement 3. Expanded representation of results in panels (c) and (d) of Figure 2.

Figure 1—figure supplement 3.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of 5 repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 4. Expanded representation of results in panels (e) and (f) of Figure 2.

Figure 1—figure supplement 4.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of 5 repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 5. Expanded representation of results in panels (g) and (h) of Figure 2.

Figure 1—figure supplement 5.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of 5 repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 6. Expanded representation of results in panels (i) and (j) of Figure 2.

Figure 1—figure supplement 6.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of five repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 7. Expanded representation of results in Figure 1.

Figure 1—figure supplement 7.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of five repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 8. Additional example of gravitational tuning in an expanded format.

Figure 1—figure supplement 8.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of five repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 9. Additional example of gravitational tuning in explanded format.

Figure 1—figure supplement 9.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of five repetitions for full scene stimuli (top) and isolated object stimuli (bottom).
Figure 1—figure supplement 10. Additional example of gravitational tuning in expanded format.

Figure 1—figure supplement 10.

The complete set of stimuli and boxcar-smoothed (across neighboring orientations) response functions for each of five repetitions for full scene stimuli (top) and isolated object stimuli (bottom).