FIG. 14. Relationship with the length-to-width ratio is examined for the optimal orientation and spatial frequency for simple cells. *A*: length-to-width ratio against the optimal orientation as a scatterplot. Circles, triangles, and square symbols indicate neurons which prefer low (<0.25 cpd), middle (≥0.25 cpd and <0.5 cpd), and high (≥0.5 cpd) spatial frequencies, respectively. Cutoff values are arbitrary. Mean length-to-width ratios were calculated for each group of cells categorized based on the optimal orientation, and were superimposed in the scatterplot by a solid curve. Error bars indicate the SDs. Receptive fields of cells pointed to by arrows (*C*–*J*) are shown in the *bottom* corresponding panels. *B*: plot of the length-to-width ratio against the optimal spatial frequency. Circles, triangles, and square symbols represent neurons tuned to horizontal (within 30° of horizontal), oblique, and vertical (within 30° of vertical), respectively. A solid curve and bars indicate the mean ± SD values of the length-to-width ratios for each population of neurons grouped on the basis of the optimal spatial frequency. Cutoff values are the same as in *A*. Neurons labeled in *A* are also indicated by arrows in *B* except for cells *D* and *E*, which are located in the dense cluster of symbols near (0.2, 1). *C*–*J*: receptive fields of simple cells that are indicated by arrows in *A* and *B*. Bright regions indicate on subregions, whereas dark regions denote off subregions. Solid ellipses indicate the extents of receptive fields determined as 5% of the peak of the fitted Gaussian envelopes. Center of each receptive field is defined as the origin. Optimal correlation delay, spatial frequency (SF), orientation (OR), and length-to-width ratio (LWR) for *C*–*J* were as follows, respectively: τ = 55, 42, 43, 54, 52, 51, 46, and 49 ms; SF = 0.32, 0.17, 0.25, 0.17, 0.98, 1.00, 0.33, and 0.50 cycles/deg; OR = 5, 38, 54, 82, 86, 135, 158, and 178°; LWR = 2.43, 1.03, 1.01, 0.73, 1.92, 1.15, 0.93, and 1.24.