"Pop-out" of targets modulated in luminance or colour: the effect of intrinsic and extrinsic uncertainty.
Targets defined by attributes such as colour or brightness are said to "pop-out" from a cluttered scene, with little or no dependency on the size of the set to be searched, while search for other attributes can depend strongly on set-size. We measured contrast thresholds for increments and decrements in luminance or colour and show that they increase strongly with set-size (as previously observed for orientation). However, in some conditions, where the potential distractors were not salient visual targets, there was no dependency of set-size at all ("pop-out"). All the data can be modelled by assuming two main sources of uncertainty: the intrinsic uncertainty due to the number of detectors monitored during a specific task and the extrinsic uncertainty introduced by increasing the number of items displayed. The strength of the effect is well explained by a simple signal detection theory "signed-max" model suited for two-tailed tasks [Journal of Vision 2 (8), 559]. The results suggest that "pop-out" is not peculiar to luminance or colour, but may occur in conditions when the intrinsic uncertainty is so high as to saturate the effects of further uncertainty sources.
Baldassi
Stefano
S
Dipartimento di Psicologia, Università di Firenze, Via di S. Niccolò, 89, 50123 Florence, Italy. stefano@in.cnr.it
Burr
David C
DC
D001288:Attention / Q000502:physiology; D003118:Color Perception / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology; D003463:Cues; D006801:Humans; D008027:Light; D008959:Models, Neurological; D008960:Models, Psychological; D009949:Orientation / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D011594:Psychometrics; D012684:Sensory Thresholds / Q000502:physiology; D017603:Signal Detection, Psychological / Q000502:physiology; D035501:Uncertainty; D014796:Visual Perception / Q000502:physiology*