approached significancep = 0.052
The interaction of the linear velocity term by treatment was not significant (χ 2 (1) < 0.001, p = 0.997); however, the interaction of the quadratic velocity term by treatment approached significance (χ 2 (1) = 3.78, p = 0.052), reflecting the fact the quadratic velocity term, and therefore the inverted-U relationship between velocity and pleasantness, was steeper in the tryptophan depletion condition than in the control condition (Fig. 4C ).