Preserved Contextual Cueing in Realistic Scenes in Patients with Age-Related Macular Degeneration.

Foveal vision loss has been shown to reduce efficient visual search guidance due to contextual cueing by incidentally learned contexts. However, previous studies used artificial (T- among L-shape) search paradigms that prevent the memorization of a target in a semantically meaningful scene. Here, we investigated contextual cueing in real-life scenes that allow explicit memory of target locations in semantically rich scenes. In contrast to the contextual cueing deficits in artificial scenes, contextual cueing in patients with age-related macular degeneration (AMD) did not differ from age-matched normal-sighted controls. We discuss this in the context of visuospatial working-memory demands for which both eye movement control in the presence of central vision loss and memory-guided search may compete. Memory-guided search in semantically rich scenes may depend less on visuospatial working memory than search in abstract displays, potentially explaining intact contextual cueing in the former but not the latter. In a practical sense, our findings may indicate that patients with AMD are less deficient than expected after previous lab experiments. This shows the usefulness of realistic stimuli in experimental clinical research.

Intact Contextual Cueing for Search in Realistic Scenes with Simulated Central or Peripheral Vision Loss.

Purpose: Search in repeatedly presented visual search displays can benefit from implicit learning of the display items' spatial configuration. This effect has been named contextual cueing. Previously, contextual cueing was found to be reduced in observers with foveal or peripheral vision loss. Whereas this previous work used symbolic (T among L-shape) search displays with arbitrary configurations, here we investigated search in realistic scenes. Search in meaningful realistic scenes may benefit much more from explicit memory of the target location. We hypothesized that this explicit recall of the target location reduces visuospatial working memory demands on search considerably, thereby enabling efficient search guidance by learnt contextual cues in observers with vision loss. Methods: Two experiments with gaze-contingent scotoma simulation (Experiment 1: central scotoma, Experiment 2: peripheral scotoma) were carried out with normal-sighted observers (total n = 39/40). Observers had to find a cup in pseudorealistic indoor scenes and discriminate the direction of the cup's handle. Results: With both central and peripheral scotoma simulation, contextual cueing was observed in repeatedly presented configurations. Conclusions: The data show that patients suffering from central or peripheral vision loss may benefit more from memory-guided visual search than would be expected from scotoma simulation and patient studies using abstract symbolic search displays. Translational Relevance: In the assessment of visual search in patients with vision loss, semantically meaningless abstract search displays may gain insights into deficient search functions, but more realistic meaningful search scenes are needed to assess whether search deficits can be compensated.

Impairment of visual memory for objects in natural scenes by simulated central scotomata.

Because of the close link between foveal vision and the spatial deployment of attention, typically only objects that have been foveated during scene exploration may form detailed and persistent memory representations. In a recent study on patients suffering from age-related macular degeneration, however, we found surprisingly accurate visual long-term memory for objects in scenes. Normal exploration patterns that the patients had learned to rereference saccade targets to an extrafoveal retinal location. This rereferencing may allow use of an extrafoveal location as a focus of attention for efficient object encoding into long-term memory. Here, we tested this hypothesis in normal-sighted observers with gaze-contingent central scotoma simulations. As these observers were inexperienced in scene exploration with central vision loss and had not developed saccadic rereferencing, we expected deficits in long-term memory for objects. We used the same change detection task as in our patient study, probing sensitivity to object changes after a period of free scene exploration. Change detection performance was significantly reduced for two types of scotoma simulation diminishing foveal and parafoveal vision--a visible gray disc and a more subtle image warping--compared with unimpaired controls, confirming our hypothesis. The impact of a smaller scotoma covering specifically foveal vision was less distinct, leading to a marginally significant decrease of long-term memory performance compared with controls. We conclude that attentive encoding of objects is deficient when central vision is lost as long as successful saccadic rereferencing has not yet developed.

Suppressive effects on motion discrimination induced by transient flankers are reduced by perceptual learning.

We investigated spatial suppression of a drifting Gabor target of 0.5 c/° induced by adjacent and iso-oriented stationary Gabors (flankers) whose spatial frequency differed by ±1 and ±2 octaves to that of the drifting target. Stimuli (target and flankers) were presented for 33 ms. Results showed greater spatial suppression when the spatial frequency of the stationary but transient flanking Gabors was either equal or 1-2 octaves lower than when it was 1-2 octaves higher than the target's spatial frequency. This asymmetry was evident only for the drifting target, but not for the stationary target. In addition, we investigated whether perceptual learning (PL) reduced the spatial suppression induced by the flankers. We found that PL increased contrast sensitivity for the target, but only when it was reduced by the lateral masking flankers, and its effect did not transfer to an isolated drifting target of equal or higher spatial frequency. These results suggest that PL selectively affects suppressive interactions rather than contrast gain. We suggest that the suppressive effect of low spatial frequency flankers and the lack of suppression with high spatial frequency flankers may reflect two complementary phenomena: camouflage by the transient flankers (i.e., context) and breaking of camouflage by form-motion segmentation. Camouflage may result because both target and flankers activate the motion (magnocellular) system. Breaking of camouflage instead may occur when target and flankers' spatial frequency are more suitable for quasi-independent activation of the form system (by the flankers) and the motion system (by the target).