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Psychophysical Consistency with Human Saliency

This page presents a collection of experimental results, obtained by application of the proposed bottom-up discriminant saliency detector (DSD) to a set of displays, classically used in psychophysical studies of human saliency and visual search.

Single and conjunctive feature search

The discriminant saliency maps are shown below each of the displays. In displays (a) and (b), targets differ from background in terms of a single basic feature (orienation (a) and color (b)), and pop-out. In display (c), the target is defined by a conjunction of orientation and color, and does not pop-out.


Search asymmetries and Weber's law

The following examples show that discriminant saliency predicts asymmetries commonly found in visual search experiments: a target pops-out if it is defined by the presence of a feature that is absent in the distractors (left display), but the reverse does not hold (right display).

Furthermore, discriminant saliency predicts the compliance of search asymmetries with Weber's law, as proposed by Treisman & Gormican (1988; Feature analysis in early vision: evidence from search asymmetries. Psychological Review, 95, 14-58, 1988). In the example below, a display is shown on the left, where the target and the distractor are both vertical segments which differ only in length. On the right, we present a scatter plot of the value of discriminant saliency as a function of the ratio DX/X (where DX is the difference between target and distractor length, and X is the distractor length), which appears in Weber's law. The dashed line shows the best fit to Weber's law.

Nonlinearities of human saliency

In this experiment discriminant saliency is measured as a function of orientation contrast (orientation difference between target and distractors). Three displays of different orientation contrast are shown in the top row. The two plots in the bottom row present the saliency measured for both human subjects (left, Figure 9 of Nothdurft (1993); The conspicuousness of orientation and motion contrast. Spatial Vision, 7, 341-363, 1993) and discriminant saliency (right). Both plots show strong threshold and saturation effects, i.e. a sigmoidal shape, showing that discriminant saliency makes accurate quantitative predictions of human saliency perception.

Distractor heterogeneity and search surface

Nothdurft (1993) showed that when the distractors in the above displays become heterogeneous, the percept of target saliency by human subjects is significantly reduced. In particular, he measured human saliency for three levels of distractor heterogeneity, using the displays shown in the top row of the following figure. The human saliency curves are shown in the left plot of the bottom row. On the right, we present the measure of discriminant saliency on these displays. Once again, discriminant saliency has a very good match to the human data.

Furthermore, by plotting the discriminant saliency curves in 3-D (left plot below), it is clear that discriminant saliency reproduces the "search surface" proposed by Duncan and Humphreys (1989; Visual search and stimulus similarity. Psychological Review, 96, 433-458, 1989), shown on the right.