Fig. 2. Method of analysis of the goldfish C-starts. (A) Superimposition of silhouettes of a goldfish during a C-start. Silhouettes were taken every 2 ms but, for clarity, only those occurring at 14-ms intervals starting at the beginning of the response are shown. The lightest image is the silhouette at the beginning of the response and it has been arbitrarily oriented with the nose (black circle) upwards. The darkest image is the fish silhouette at approximately 104 ms after the stimulus delivery. (B) Superimposition of midlines determined from silhouette images. The silhouettes were reduced to a midline a single pixel thick using a thinning algorithm. For clarity, every fourth midline is shown (i.e. every 8 ms). The first midline is at the start of the response. (C) The rostral portion of each midline, corresponding to the rostral 40% of the midline (Nissanov, 1991). Regression lines are shown in 2 ms increments. The regression line that begins stage 2 and the line 70 ms after the start are labeled. The angle at the beginning of stage 2 is formed between the regression line at start and the regression line at the stage 2 latency. The escape trajectory angle (ETA) is formed between the regression line at start and the regression line 70 ms later. The straight-line distance that the center of mass travels during 70 ms after the start is delineated as well.