FIGURE 1

Metrics to quantify orientation selectivity in neural responses. (A) Tuning curves of neural responses to oriented visual stimuli. The color coding indicates different levels of orientation selectivity, from low (yellow) to high (magenta). The preferred orientation angle (𝜃_preferred) corresponds to the angle of the stimulus eliciting maximal responses. The orthogonal orientation angle (𝜃_orthogonal) corresponds to angles of stimuli oriented ± 90° relative to the preferred orientation angle. (B) Response profiles to oriented visual stimuli corresponding to the tuning curves represented in (A). The orientation and direction of movement of square-wave gratings with 30° angular distance steps are indicated around. (C) Metrics typically used to quantify orientation selectivity in neural responses: orientation selectivity index (OSI; left), and vector length in orientation space (L_ori also known as 1 – circular variance; right). Quantification of orientation selectivity for the responses in (A,B) is reported in the middle. Note that the two metrics have different sensitivities to tuned firing. The OSI consists in the difference between responses to preferred, R(𝜃_pref), and orthogonal, R(𝜃_orth), stimuli divided by their sum. On the other hand, L_ori takes as input responses to all orientation angles, R(𝜃_k), in order to calculate the mean vector length in orientation space (k ranges from 0° to 180°). See Mazurek et al. (2014) for detailed descriptions and comparisons of the two metrics.