On the use of the Ternus test to assess magnocellular function.

Ternus stimuli give rise to two mutually exclusive visual experiences: with long interstimulus intervals (ISIs) the elements in the stimulus are perceived as moving together as a group ('group movement'), while at shorter ISIs only a single element appears to be moving ('element movement' or 'end-to-end movement'). It has been hypothesized that group and element movements, respectively, reflect magnocellular and parvocellular activity. On this basis, Ternus tests have been used to assess magnocellular function in dyslexic individuals. This use of Ternus stimuli is examined in the present report. On the basis of amplitude spectra of the stimuli and of a review of previous studies it is concluded that to use Ternus tests to assess magnocellular function is problematic.