The Effect of the Nature of the Surround on the Perceived Lightness of Grey Bars within Square-Wave Test Gratings

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Abstract
The perceived lightness of grey bars within grey–white and grey–black square-wave test gratings was measured in the presence of different surrounding regions (plain black, plain white, or black–white square-wave gratings). The results for the grey–white test gratings are explained in terms of three separate processes: (i) lightness contrast; (ii) lightness assimilation resulting from the limited ability of the visual system to deal with grating contrast at higher spatial frequencies; and (iii) lightness assimilation resulting from lateral inhibition between pattern detecting channels mediating the perception of the gratings in the test regions and the surrounds. The results for the grey–black test gratings were explained without reference to the third process. It is concluded that techniques involving lightness assimilation could provide investigators with a sensitive new method of investigating the specificities of the inhibitory interactions underlying pattern perception.