D. Alexander Varakin

Scene structure enhances change detection

Theories of objects recognition, scene perception, and neural representation of scenes imply that jumbling a coherent scene should reduce change detection. However, evidence from the change detection literature questions whether jumbling affects change detection. The experiments reported here demonstrate that jumbling does, in fact, reduce change detection. In Experiments 1 and 2, change detection was better for normal scenes than for jumbled scenes. In Experiment 3, inversion failed to interfere with change detection, demonstrating that the disruption of surface and object continuity inherent to jumbling is responsible for reduced change detection. These findings provide a crucial commonality between change detection research and theories of scene perception and neural representation. We also discuss why previous research may have failed to find effects of jumbling.

Implicit learning for probable changes in a visual change detection task.

Previous research demonstrates that implicitly learned probability information can guide visual attention. We examined whether the probability of an object changing can be implicitly learned and then used to improve change detection performance. In a series of six experiments, participants completed 120-130 training change detection trials. In four of the experiments the object that changed color was the same shape (trained shape) on every trial. Participants were not explicitly aware of this change probability manipulation and change detection performance was not improved for the trained shape versus untrained shapes. In two of the experiments, the object that changed color was always in the same general location (trained location). Although participants were not explicitly aware of the change probability, implicit knowledge of it did improve change detection performance in the trained location. These results indicate that improved change detection performance through implicitly learned change probability occurs for location but not shape.

The effect of scene structure on time perception

The current experiments examined the hypothesis that scene structure affects time perception. In three experiments, participants judged the duration of realistic scenes that were presented in a normal or jumbled (i.e., incoherent) format. Experiment 1 demonstrated that the subjective duration of normal scenes was greater than subjective duration of jumbled scenes. In Experiment 2, gridlines were added to both normal and jumbled scenes to control for the number of line terminators, and scene structure had no effect. In Experiment 3, participants performed a secondary task that required paying attention to scene structure, and scene structures effect on duration judgements reemerged. These findings are consistent with the idea that perceived duration can depend on visual–cognitive processing, which in turn depends on both the nature of the stimulus and the goals of the observer.

Object appearance and picture-specific viewpoint are not integrated in long-term memory.

Previous work has demonstrated that visual long-term memory (VLTM) stores detailed information about object appearance. The current experiments investigate whether object appearance information in VLTM is integrated within representations that contain picture-specific viewpoint information. In three experiments using both incidental and intentional encoding instructions, participants were unable to perform above chance on recognition tests that required recognizing the conjunction of object appearance and viewpoint information (Experiments 1a, 1b, 2, and 3). However, performance was better when object appearance information (Experiments 1a, 1b, and 2) or picture-specific viewpoint information (Experiment 3) alone was sufficient to succeed on the memory test. These results replicate previous work demonstrating good memory for object appearance and viewpoint. However the current results suggest that object appearance and viewpoint are not episodically integrated in VLTM.

Intentional Memory Instructions Direct Attention But Do Not Enhance Visual Memory

The current experiment investigated the role of intentional-encoding instructions and task relevance at study on visual memory performance. Task relevance was manipulated by having participants keep a running tally of either the to-be-remembered objects or an irrelevant category of objects during study. Half of the participants within each level of task relevance were further instructed to remember one category of objects for a subsequent recognition test, and the other half of the participants were not informed of a memory test. Intentional-encoding instructions improved recognition discrimination only when participants were not already keeping a tally of the to-be-remembered objects. This result suggests that intentional-encoding instructions may improve visual memory via generic attentional modulation, not encoding-specific processes.