Figure 2.

The Distance-Discrimination Function

(A) Movement traces depicting the position of a single Canton-S fly in a behavioral chamber (horizontal dimension) as a function of time (vertical dimension). The same fly was tested between a common reference odor, 1-octanol (orange), and the indicated test odors (blue). The data are arranged by increasing Euclidean and cosine distances between the respective ePN activity vectors.

(B) Decision bias scores of 20 Canton-S flies tested against seven odor combinations. Orange symbolizes a preference for 1-octanol, and blue symbolizes a preference for the comparison odor; the intensity of shading represents the magnitude of bias according to the key on the left.

(C) Absolute magnitude of the decision bias scores depicted in (B). The intensity of shading represents the magnitude of bias according to the key on the left.

(D) Absolute decision bias scores elicited by 51 odor pairs as functions of Euclidean (left) and cosine (right) distances between ePN signals (mean ± SEM, n = 40–80 flies per data point). The distance-discrimination functions (dotted lines) were obtained from least-squares logistic fits to the data; the fits were constrained to include the origin (Euclidean distance: R² = 0.6577, p < 0.0001; cosine distance: R² = 0.6693, p < 0.0001). Shading indicates the area bounded by the distance-discrimination function where decision bias scores are predicted to fall. See also Table S1.

(E) Absolute decision bias scores elicited by 36 odors against air (red) as functions of Euclidean (left) and cosine (right) distances between ePN signals (mean ± SEM, n = 40–80 flies per data point). ePN signals in air were calculated from measured spontaneous ORN activity (Hallem and Carlson, 2006; Hallem et al., 2004). The distance-discrimination function and experimental measurements obtained in (D) are reproduced for comparison (gray).

See also Table S2 and Figure S2.