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First published online October 18, 2006
Journal of Experimental Biology 209, 4339-4354 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02517
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A `bright zone' in male hoverfly (Eristalis tenax) eyes and associated faster motion detection and increased contrast sensitivity

Andrew D. Straw1,*, Eric J. Warrant2 and David C. O'Carroll1

1 Discipline of Physiology, School of Molecular and Biomedical Science, The University of Adelaide, SA 5005, Australia
2 Vision Group, Department of Cell and Organism Biology, Lund University, Lund, Sweden


Figure 1
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  		Fig. 1. Optical characteristics of Eristalis tenax eyes showing the `bright zone' of males, in which facet diameter is maximal in the fronto-dorsal eye but is not associated with smallest interommatidial angle. Interommatidial angles are given as the average of the angles across horizontal and vertical sampling baselines. Data are from a single male and single female fly and in close agreement with data from the other fly tested of each sex. f=frontal, d=dorsal, l=lateral.

 

Figure 2
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  		Fig. 2. Local preferred directions (LPD) and local motion sensitivities (LMS) of Eristalis LPTCs. The direction of the arrow indicates the LPD and the magnitude gives the LMS, as defined in the Materials and methods. The origin of the arrows is displayed on a Mercator projection, but the direction and magnitude are displayed using Euclidian geometry to facilitate LMS comparison (male HSN, N=3; female HSN, N=5; male HSNE, N=3; female HSNE, N=5). HSN, HSNE, horizontally sensitive N, NE neurones.

 

Figure 3
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  		Fig. 3. Response as a function of contrast of Gaussian windowed sinusoidal grating (Gabor patch). (A) Single trials showing responses to traditional `contrast step' stimulus. (B) `Contrast ramp' stimulus measures contrast-response relationship more rapidly. Blue line shows mean response and gray fill shows mean response ± instantaneous s.d. (C) Comparison of methods shown in A and B plotted on logarithmic contrast axis. Smooth red line shows analytic fit to contrast ramp data. Data are from frontal portion of the receptive field of a single male HSN cell viewing sinusoidal grating at 0.1 cycles deg.-1 at 5 Hz. Values are means ± s.d. from at least 3 trials. Az, azimuth; El, elevation.

 

Figure 4
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  		Fig. 4. Summary of contrast-response relation under several conditions showing that the contrast ramp method estimates contrast sensitivity similarly to the contrast step method, but much more quickly. Data analyzed as in Fig. 3C. All parameters as listed, spatial frequency= 0.1 cycles deg.-1. (A-E) Data from two HSNE cells from several retinal locations. (F) HSN cell from Fig. 3 viewing laterally positioned grating. All data from male flies. Values are means ± instantaneous s.d. from a minimum of 3 trials. Az, azimuth; El, elevation.

 

Figure 5
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  		Fig. 5. Responses to contrast ramp stimulus at a range of temporal (TF) and spatial frequencies (SF) in the frontal portion of the receptive field of a single male HSN neuron. The mean response to 3 or more trials is shown in black for each combination of spatial and temporal frequency as plotted as in Fig. 3C. Parameter fits are shown in red. The data are plotted on logarithmic contrast axis. Minimum of 3 trials per trace; azimuth=0°, elevation=60°. Details of fitting described in Materials and methods. Decade C, tenfold Michelson contrast variation.

 

Figure 6
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  		Fig. 6. Contrast-response surfaces of a single male HSN cell showing faster temporal dynamics and higher spatial frequency tuning in the frontal portion of the receptive field. The thick gray line in each panel is an iso-velocity line at the preferred velocity, the optimal temporal frequency (TF) divided by the optimal spatial frequency (SF). (A) Data are from the frontal portion of the receptive field, azimuth=0°, elevation=60°. (B) Data are from the lateral portion of the receptive field, azimuth=90°, elevation=60°. Height of surface is the estimated response to a grating of Michelson contrast 1.0 based on fit parameters calculated at each spatial and temporal frequency. Fit parameters for A are shown in Fig. 5. Contour interval=1.0 mV, with negative responses dotted.

 

Figure 7
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  		Fig. 7. Comparison of temporal frequency (TF) tuning at two receptive field locations of HSN cells showing sexually dimorphic contrast sensitivity and temporal dynamics. Frontal receptive field (A,C,E) for HSN cells is defined as 0° azimuth and 60° elevation. Lateral receptive field (B,D,F) is defined as 90° azimuth and 60° elevation. Responses were estimated for Michelson contrasts 1.0 (A,B) and 0.2 (C,D) and the contrast sensitivity was calculated for a criterion response of 2 mV (E,F). Estimated response and contrast sensitivity were calculated from contrast ramp data (for details see Materials and methods). Spatial frequency 0.1 cycles deg.-1. Values are means ± s.e.m.; males, N=5 (filled squares), females, N=6 (open circles).

 

Figure 8
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  		Fig. 8. Comparison of spatial frequency (SF) tuning at two receptive field locations of HSN cells showing sexually dimorphic contrast sensitivity and lateral spatial frequency tuning. Estimated contributions from Type 1 and Type 2 EMDs are given as arrow thickness and again as the height of small bars. EMD contributions and smooth curves were fit to the shown data with a two EMD model constrained by interommatidial angle data taken from Fig. 1. Free parameters were total gain, relative EMD contribution, and saturation. These parameters can be found in Table 1. Temporal frequency 5 Hz. Values are means ± s.e.m.; males, N=5 (filled squares), females, N=6 (open circles).

 

Figure 9
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  		Fig. 9. Comparison of temporal frequency (TF) tuning at two receptive field locations of HSNE cells showing little sexually dimorphic contrast sensitivity or temporal dynamics. Spatial frequency 0.1 cycles deg.-1. Values are means ± s.e.m.; males, N=4 (filled squares), females, N=5 (open circles).

 

Figure 10
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  		Fig. 10. Comparison of spatial frequency tuning at two receptive field locations of HSNE cells showing little sexually dimorphic contrast sensitivity and lateral spatial frequency tuning. Temporal frequency 5 Hz. Values are means ± s.e.m.; males, N=4 (filled squares), females, N=5 (open circles).

 




© The Company of Biologists Ltd 2006