The Recognition of Solid Object Shape: The Importance of Inhomogeneity

Aging and temporal integration in the visual perception of object shape

It has been known for more than 160 years that highly occluded objects that would normally be visually unrecognizable can be successfully identified when they move. This anorthoscopic perception relies on the visual system's ability to integrate information over time to complete the perception of an entire object's shape. In this experiment, 16 younger and older adults (mean ages were 20.5 and 74.6 years, respectively) were familiarized with the (unoccluded) shapes of five naturally-shaped objects (bell peppers, Capsicum annuum) until they could be easily identified (i.e., with accuracies of at least 90 percent correct). All observers then viewed the stimulus objects anorthoscopically as they moved behind narrow slits; only small object fragments could be seen at any given time, because the objects were almost totally occluded from view. Even though the object identification performance for all observers was equivalent when whole object shapes were visible, a large age-related deficit in object identification emerged during anorthoscopic viewing such that the younger adults' identification performance was 45.4 percent higher than that of the older adults. This first ever study of aging and anorthoscopic perception demonstrates that there is an age-related deficit in performing the temporal integration needed for successful object recognition.

Aging and haptic shape discrimination: the effects of variations in size

Seventy-two older and younger adults haptically discriminated the solid shape of natural objects (bell peppers, Capsicum annuum). Plastic copies of the original-sized fruits were used as experimental stimuli, as well as copies that were reduced in size to 1/8th and 1/27th of the original object volumes. If haptic object shape is represented in a part-based manner, then haptic shape discrimination performance should be at least partly size invariant, since changes only in scale do not affect an object’s constituent parts. On any given trial, participants sequentially explored two bell pepper replicas and were required to judge whether they possessed the same shape or had different shapes. For some participants, the objects to be discriminated possessed the same size, while for others, the two objects had different sizes. It was found that variations in scale did significantly reduce the participants’ haptic sensitivities to shape. Nevertheless, the discrimination performance obtained for large variations in size was no lower than that obtained for smaller variations in size. The results also demonstrated that increases in age modestly affect haptic shape discrimination performance: the d′ values of the older participants were 15.5% lower than those of the younger participants.