Volume 1
A text-book of experimental psychology : with laboratory exercises / by Charles S. Myers.
- Charles Samuel Myers
- Date:
- 1911
Licence: Public Domain Mark
Credit: A text-book of experimental psychology : with laboratory exercises / by Charles S. Myers. Source: Wellcome Collection.
96/370 page 76
![For example, a given patch of grey or of colour tends to be tinged in the colour complementary to that stimulating the rest of the retina ; this is known as ‘ colour contrast ’ (exps. 57-60). It is most evident when the contrasting sensations are of equal brightness (exp. 59). Again, a given surface (coloured or colourless) appears brighter or darker than it would otherwise appear according as it is brighter or darker than a neighbouring surface ; this is known as ‘ brightness contrast ’ (exps. 61-63). Brightness contrast rapidly diminishes with increase of the distance between the two surfaces. Consequently, it is much more obvious when the one surface is smaller than, and completely surrounded by, the other, than when the two surfaces are equal and placed side by side. It can be experimentally shown that what is gained in brightness, by the one surface is lost by the other. Brightness contrast is thus clearly due to mutual interaction in neighbouring retinal areas. Brightness contrast is of course especially well-marked at the adjoining margins of the two surfaces. Here it sub¬ serves the important biological function of sharply outlining seen objects. For the retinal images of external objects must always have more or less ill-defined borders owing to the inevitable irradiation of light rays. Both brightness contrast and colour contrast may be intensified by increasing the extent or saturation of the larger surface, or by obliterating (eg. by aid of the colour wheel) any differences in texture and the like between the two surfaces so that they appear as a single surface instead of as two separate surfaces. [.Simultaneous and Successive Induction.—But these effects of simultaneous contrast disappear on prolonged fixation and are replaced by others of a directly opposite character. The surface, which at the beginning of fixation had evoked a contrast colour or brightness, now induces its own colour or brightness. This is termed ‘ simultaneous induction.’ Corre¬ sponding changes in the after-image are termed ‘ successive induction ’ (exp. 74).] Spectral Colour Mixtures.—We have seen (page 72) that](https://iiif.wellcomecollection.org/image/b3135984x_0001_0096.jp2/full/800%2C/0/default.jpg)
