The representation of unseen objects in visual neglect: Effects of view and object identity

Abstract

We provide evidence for long-term priming based on view-specific representations of neglected stimuli. A patient with visual neglect, M.P., was asked to search for a target presented amongst other objects on a table. Subsequently recognition memory was tested for items that were identified and for items missed in search. Items that were missed were rejected more slowly than novel items in the recognition memory task, providing evidence for implicit processing (Experiment 1). Implicit memory for missed items was both item-specific (Experiment 2) and view-specific (Experiment 3), and it was eliminated when there were intervening activities lasting about 1 hour (Experiment 4). There was also an implicit memory for distractors in the search task, which was item- but not view-specific (Experiments 2 and 3) and it lasted for at least an hour, even with other intervening activities (Experiment 4). The data suggest that the representations of neglected stimuli may differ qualitatively from those of nonneglected items, with representations of neglected objects being both view-specific and vulnerable across extended retention intervals. The results support the argument that attention is needed in order to encode object representations that are robust to view transformations and temporal decay or interference.

Keywords:

• Visual neglect
• object recognition
• viewpoint invariance

The work was supported by grants from the Medical Research Council and the Stroke Association to Glyn Humphreys. We thank M.P. for his kind participation.

Notes

¹ The effect of position has been calculated between left and right objects only, without the central position, because for each trial we had two objects that were present but not prompted on the left and two on the right, but only one in the centre.

² Note that “novel” items and “target-absent” items have no position.

³ To ensure that the data on implicit priming were not affected by M.P.'s learning the objects, we also replicated the data in Experiment 4 using a new set of stimuli. Consistent with M.P.'s episodic memory improving due to familiarity with the objects, his explicit recognition memory for detected objects was reduced when a novel object set was used (he responded “old” to 28/45, i.e., 62%, of the targets detected in the study phase). Explicit memory now did not differ from that in Experiment 1 (χ² < 1.0). However, the data on implicit memory matched those in Experiment 4.