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Irina M. Harris, Paul E. Dux; Probing the nature of object representations with repetition blindness for rotated objects. Journal of Vision 2004;4(8):506. doi: https://doi.org/10.1167/4.8.506.
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We addressed the question of whether object recognition is orientation-invariant or orientation-dependent using a repetition blindness (RB) paradigm. RB manifests as a reduction in the ability to report a repeated stimulus if it occurs within ~400 ms of the first occurrence of the item, and is usually interpreted as a failure to assign distinct episodic tokens to the same visual type. This makes RB an ideal tool with which to investigate what kinds of representations are treated as the same by the visual system. We tested whether RB can be obtained for repeated objects (with or without a usual upright orientation) that were presented either in identical orientations or differed by 30, 60, 90, or 180 . Significant RB was obtained for all orientation conditions, consistent with the idea that early stages of object recognition are mediated by orientation-invariant representations. However, RB was often reduced when objects with a usual upright orientation were presented upright and upside-down. An additional experiment showed that the 0 and 180 orientations are determined more easily than other orientations. This appears to help subjects encode the repeated objects as different episodes, and thus reduces susceptibility to RB. The results indicate that, although object recognition is mediated by orientation-invariant representations, orientation plays an important role in establishing distinct episodic representations of objects, enabling one to report them as separate events. They also suggest that the usual upright orientation of an object — if it exists — is stored in memory and primes orientations in which the top-bottom axis of the object is aligned with that stored in memory.
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