Cite as:
Lingelbach B, Ehrenstein W H, 2005, "Adding diagonals to the scintillating grid" Perception 34 ECVP Abstract Supplement

Adding diagonals to the scintillating grid

B Lingelbach, W H Ehrenstein

Recently, Geier et al (2004 Perception 33 Supplement, 53) reported that the Hermann grid illusion disappears with simple sinoid distortion of the grid, an observation that cannot be easily reconciled with an explanation based on concentric receptive fields of retinal ganglion cells as proposed by Baumgartner's model. Rather, it favours (additional) cortical mechanisms, as suggested before, Lingelbach et al (1985 Perception 14 Supplement, 7), who showed that the Hermann grid illusion disappears if diagonals are added to the orthogonal grid (for a review see Spillmann, 1994 Perception 23 691 - 708). We investigated whether adding diagonals to the scintillating grid would likewise weaken or extinguish its strong illusion. A grid (15 deg × 15 deg) showing an optimal scintillating effect--matrix of 9 × 9 black squares, separated by orthogonal medium-grey lines (10 min of arc width) with white dots (15 min of arc diameter) at their intersection--served as reference pattern (A). Diagonals inserted in A were either of the same width as the orthogonal grid bars (B) or thinner: 0.5 (C) or 0.2 (D) times their width. In addition, patterns B - D were modified in that the diagonals were sinusoidally curved leaving the intersections right-angled (E - G). Six observers judged the strength of the scintillating illusion in the modified patterns relative to reference A (100%). The scintillating effect was virtually absent in patterns B (8%) and E (3%) and still markedly reduced with thinner, straight (C, D) or curved (F, G) diagonals, illusory magnitudes ranging from 18% to 32%. Our results show that the above-mentioned influence of diagonals on the Hermann grid also strongly affects the scintillating grid, hence suggesting the involvement of orientation-sensitive cortical mechanisms.

[Supported by ZVA (Zentralverband der Augenoptiker Deutschlands).]

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