Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2007 Feb 28;2(2):e256.
doi: 10.1371/journal.pone.0000256.

The Lingering Effects of an Artificial Blind Spot

Affiliations
Free PMC article

The Lingering Effects of an Artificial Blind Spot

Michael J Morgan et al. PLoS One. .
Free PMC article

Abstract

Background: When steady fixation is maintained on the centre of a large patch of texture, holes in the periphery of the texture rapidly fade from awareness, producing artificial scotomata (i.e., invisible areas of reduced vision, like the natural 'blind spot'). There has been considerable controversy about whether this apparent 'filling in' depends on a low-level or high-level visual process. Evidence for an active process is that when the texture around the scotomata is suddenly removed, phantasms of the texture appear within the previous scotomata.

Methodology: To see if these phantasms were equivalent to real low-level signals, we measured contrast discrimination for real dynamic texture patches presented on top of the phantasms.

Principal findings: Phantasm intensity varied with adapting contrast. Contrast discrimination depended on both (real) pedestal contrast and phantasm intensity, in a manner indicative of a common sensory threshold. The phantasms showed inter-ocular transfer, proving that their effects are cortical rather than retinal.

Conclusions: We show that this effect is consistent with a tonic spreading of the adapting texture into the scotomata, coupled with some overall loss of sensitivity. Our results support the view that 'filling in' happens at an early stage of visual processing, quite possibly in primary visual cortex (V1).

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1
Stimuli for adaptation (a) and test (b) phases of the main experiment. When the observer indicates that the two blank areas have faded from view, the adapting stimulus is replaced for 100 ms with the test stimulus. The observer's task is to decide which of the two test patches (left or right) has the higher contrast. When one of the tests has zero contrast, the task is one of simple detection. Otherwise, it is contrast discrimination.
Figure 2
Figure 2
Results of main experiment. Each row shows results for a different observer. The data points are the 82%-correct thresholds derived from psychometric functions, with error bars representing 95% confidence intervals derived from a bootstrap procedure. In the left-hand panels, circles show contrast-discrimination functions in the baseline condition without adaptation. The leftmost point is the detection threshold, at zero pedestal contrast. Boxes show thresholds obtained with a 100%-contrast adapting stimulus. The right-hand panels show how simple detection thresholds (vertical axis) vary as a function of adapting contrast (horizontal axis). The solid curves show best fits of a 6-parameter model, in which sensitivity and ‘filling in’ were allowed to vary with adapting contrast.
Figure 3
Figure 3
Left panel: The dipper function for MJM at three different levels of adapting contrast (diamonds, squares and circles for adapting contrast 0, 0.3 and 1.0 respectively). Horizontal axis: pedestal contrast; vertical axis, performance threshold. Middle panel: effects of different levels of adapting contrast (horizontal axis) on thresholds at two levels of pedestal contrast (squares and circles). Right panel: Effects of pedestal contrast on contrast discrimination for a 2 cpd/4 Hz drifting Gabor pattern, in the presence (circles) and absence (boxes) of superimposed dynamic noise masks (as in Fig 1b).
Figure 4
Figure 4
Results of a dichoptic experiment in which the adapting stimulus was in one eye while the other eye saw a blank field. Thresholds as a function of pedestal contrast were then obtained either in the adapted eye or the non-adapted eye. The left-hand panels show the mean (across eyes) for the adapted and non-adapted conditions. The continuous lines are maximum-likelihood fits to these data using the model described in Methods. The effect of adaptation is similar to that of a lower contrast binocular adapter (Fig. 3, top panel). Note that adaptation improves detection performance (leftmost point) in both observers. The right-hand panel shows the difference in threshold between the adapted and the non-adapted eye, in the adapted condition. There is evidence for slightly greater masking at high pedestal levels in the adapted eye, but not at low and intermediate pedestal contrasts.

Similar articles

See all similar articles

Cited by 5 articles

References

    1. Troxler D. Uber das Verschwindern gegebener Gegenstande innerhalb unsers Gesichtskrcises. 1804 n Ophthalmologisches Bibliothek, Vol II Edited by K Himley and J A Schmidt Jena: Fromann, 51–53.
    1. Lou L. Selective peripheral fading: evidence for inhibitory sensory effect of attention. Perception. 1999;28:519–526. - PubMed
    1. Pessoa L, Thompson E, Noe A. Finding out about filling-in: a guide to perceptual completion for visual science and the philosophy of perception. Behav Brain Sci. 1998;21:723–748. discussion 748–802. - PubMed
    1. Ramachandran VS, Gregory RL. Perceptual filling in of artificially induced scotomas in human vision. Nature. 1991;350:699–702. - PubMed
    1. Campbell FW, Kulikowski JJ. Orientation selectivity of the human visual system. Journal of Physiology. 1966;187:437–445. - PMC - PubMed

Publication types

Feedback