cases, the 90% confidence bands include the origin, which was also 

 predicted by equation 2. We tested data for various days and models, 

 and found that the slopes of T vs 1/V lines were approximately the 

 same as the mean reaction distances for the same data in D vs V 

 plots. The three pairs of graphs in Fig. 1 are representative of 

 the fits obtained, and justify the use of reaction distance as a 

 single parameter which expresses the strength of the escape reaction 

 elicited by a given model. Below, we will compare this parameter of 

 strength by Student's t tests. Comparisons are only made in cases 

 for which F tests showed the variances of the two sets of data not 

 to differ. We will compare reaction distances for experiments 

 conducted on different days, because we found that reaction distance 

 did not differ significantly from day to day. 



Size and Shape 



Table 1 shows averages for reaction distance for models of different 

 shapes and sizes. By ranking the models according to this parameter 

 it is seen that there is no significant difference between shapes 

 which is consistent for all sizes. But the ranked data for different 

 shapes shows the same order for all sizes in all cases. This would 

 happen by chance less than 0.37o of the time; the trend toward greater 

 reaction distance with increasing size is therefore highly significant. 

 One cannot, however, distinguish between a logarithmic and a linear 

 relation between area and effectiveness. 



TABLE 1 



Small: Medium: Large: 



Shape Area = 100 Area = 200 Area = 400 



Ellipse 1.00+ 0.22 1.23+ 0.17 1.26+ 0.34 



Circle 0.79+ 0.12 l.lfrf 0.22 1-27+ 0,24 



Square 0.85+ 0.18 1.15rf 0.38 1.43+ 0.43 



Table 1: mean reaction distance + 95% confidence limits for 

 white models of different size and shape. The matrix of 

 ranks shows a significant size trend, but no shape trend. 



Color 



In a series of experiments designed to test whether the fish pay 

 attention to color or contrast, a series of medium ellipses were 

 painted different colors. We found that light colored models did not 

 differ significantly from each other (white, silver, yellow). Simi- 

 larly, dark colored models did not differ from each other (red, 

 black). A Student's t test comparing lumped dark to lumped light 



VI-204 



