Fig. 2.

Schematic representations of the stimuli in the 20 conditions (depicted with the target on the left). The luminance of both the target and the references is 5.1 cd/m² and they are both 1 cm² gray squares unless otherwise mentioned (see “relevant details”). a The 13 conditions that were performed by all participants. Red lettering indicates that the responses depend on attributes that are normally needed to recognize objects, and blue lettering indicates that all items change. b The seven additional luminance conditions that were performed by six participants (numbers between brackets are the percentage that the references are brighter than the target)