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The γ * π 0 → γ form factor, including the extension off the pion massshell, is obtained from a generalized impulse approximation within a QCDbased model field theory known to provide an excellent description of the pion charge form factor. This approach implements dressing of the vertex functions and propagators consistent with dynamical chiral symmetry breaking, gauge invariance, quark confinement and perturbative QCD. Soft nonperturbative behavior, dictated by the axial anomaly, is found to evolve to the perturbative QCD limit only for Q 2 ≥ 20 GeV 2 .

The quark-loop contribution to the ρ 0 − ω mixing self-energy function is calculated using a phenomenologically successful QCD-based model field theory in which the ρ 0 and ω mesons are compositeqq bound states. In this calculation the dressed quark propagator, obtained from a model Dyson-Schwinger equation, is confining. In contrast to previous studies, the meson-qq vertex functions are characterised by a strength and range determined by the dynamics of the model; and the calculated off-mass-shell behaviour of the mixing amplitude includes the contribution from the calculated diagonal meson self-energies. The mixing amplitude is shown to be very sensitive to the small isovector component of dynamical chiral symmetry breaking. The spacelike quark-loop mixing-amplitude generates an insignificant charge symmetry breaking nuclear force.

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In Experiment I, three groups of 20 Ss each were exposed to a light of 550 mt (yellowish-green) for 60 sec and then viewed a random sequence of wavelengths with instructions to respond only to the original color. The instructions given the three groups were worded differently in an attempt to vary the strength of a set-to-discriminate assumed to be created by this procedure. The three groups produced similar gradients, each with a peak of responding at 540 my, in agreement with Kalish's (1958) published gradient for the 550 my standard stimulus value. It was suggested that the nature of the task is such that a strong discriminatory set is produced regardless of the wording of the instructions.A temporal analysis of the gradient as it develops during the testing revealed that initially the peak of responding occurs at 550 my; but as testing progresses, it shifts gradually in the direction of the shorter wavelengths (purer greens). Experiment II was performed to test the generality of the phenomenon of regression to the primary color. Two groups of 20 Ss each were tested for generalization following exposure to 510 m/A (bluish-green) and 525 my (pure green), respectively. We predicted that the 510 m/A gradient would reveal a progressive shift toward the longer wavelengths (purer greens), whereas the 525 m, gradient would show no tendency to shift. The results were strikingly in accord with these predictions.We concluded that although a physiological process could not be ruled out, the verbal labeling of the standard stimulus value may well be responsible for the regression of the gradient toward the primary color.