79, which differed significantly from chance, t(13) = 3.92, p = .002. Infants produced an average of approximately 1.5 additional vocalizations during the impossible cube display above that of the possible cube display and the perceptual controls. This pattern of behavior was consistent in 10 infants, with two infants vocalizing equally and two infants vocalizing more during the possible cube display, Z = 2.72, p = .007. By contrast,

there were no reliable differences in vocalizations made during presentation of the possible cube versus the other perceptual control stimuli (all p-values > .68). The frequency of infants’ mouthing behavior toward each of the displays was also PD0332991 datasheet recorded. Interestingly, five infants engaged in mouthing behavior, Mitomycin C ic50 but only toward the impossible cube display, t(13) = 2.69, p < .02, and they did not use oral exploration for any of the other displays. This pattern of behavior was consistent in five of the infants, and nine infants did not engage in any attempted mouthing behavior, Z = 2.24, p = .02. We set out to examine the effects of a perceptual illusion on infants’ manual exploration. Our initial question of whether 9-month-olds would respond differently to picture displays of possible and impossible cubes received a

clear answer: Infants engaged in qualitatively similar types of reaching behaviors (e.g., touching, scratching, rubbing, and patting) toward the possible and impossible cubes as well as the nonobject pictorial control displays, but they directed a significantly greater number of these gestures toward the impossible object display. Thus, by 9 months of age, infants

use the pictorial depth cue of interposition to guide manual investigation of 2D depictions of objects, and they behave differently in response to pictures of possible and impossible objects. Presumably, it was the detection of anomalous depth information that inspired greater visual attention and more persistent manual exploration of the pictures of impossible objects. Perhaps the impossible figure invoked increased interest and exploration because the infants found the unusual geometry so novel and unlike any other objects they Teicoplanin had previously encountered in the world. The impossible cube display also elicited a reliably higher frequency of social referencing to the parent and experimenter, as well as a significantly greater number of vocalizations relative to the possible cube and perceptual control displays. Increased referential looking to the mother (a trusted source) and to the experimenter (a friendly female stranger in close proximity) may be due to the infants’ desire to gather applicable information about the unusual or ambiguous nature of the impossible cube stimulus.