Iconic memory, color discrimination and contrast detection
This thesis consists of three separate psychophysical studies. The first study investigates the role of selective and nonselective transfer processes in partial reports of information from briefly exposed letter arrays using a partial report-plus-mask paradigm. The data obtained allow a decomposition into nonselective and selective transfer, and provide evidence for algebraic addition of the two processes. We present a model which describes the data, as well as partial report data without masks and whole report data from a control condition.
The second study shows the effect of the state of adaptation on color discrimination. We measured discrimination thresholds under two different states of adaptation of the eye. Under one condition, the observer is adapted to the color where thresholds are measured. Under the other we measure thresholds while the observer is adapted to an equal energy white. Discriminability is always better in the first case. The results seem to be mediated by two independent mechanisms which are sensitive to the cardinal directions of color space.
The third study investigates processing of luminance and chromatic signals by the visual system. We find that the efficiency with which the visual system detects a sine-wave pattern in broad-band spatio-temporal noise is the same for luminance and chromatic inputs. Furthermore, a luminance mask does not affect thresholds for chromatic signals and vice versa, indicating that there are no interactions between processing of the two. We measure spectral tuning curves in a variety of directions of color space. These imply the existence of mechanisms sensitive to weighted sums of luminance and chromatic inputs.