Attentional perceptual thresholds for manipulated digitized mammograms

This paper describes a series of experiments to investigate influence of perceptual response in skilled observers, due to subtle pixel intensity transforms in radiological images. Contrast and edge enhancement operations were applied to digitized mammograms. in order to determine thresholds at which variations in attentional behaviour not consciously identified by the observer were detected, during normal visual scanning procedures in a typical screening viewing situation. Continuous tracking of eye movements was undertaken to obtain patterns of fixation sequences and durations for three different observers, and both qualitative and quantitative analyses were applied to this data. Consistent thresholds at which attentional perturbation occurred were established based on levels of aggregated pixel errors determined by SNR values, across the different methods of image manipulation considered.