Letter identification in words and non-words, with variation in visual angle and delay of position cue.

Two experiments are described in which subjects were required to report the name of a single position-cued 'critical' letter in a tachistoscopically displayed string of four letters. The stimulus characters were arranged to form three types of letter strings: (i) strings in which the letters did not form words; (ii) words in which contextual constraint of the critical letters was minimised; and (iii) words in which contextual constraint of the critical letters was maximised. The serial position of the letter to be identified in each string was cued at delays of -500, -100, and +500 ms, in experiment 1 and at delays of -510 and +510 ms in experiment 2, and in both experiments one group of subjects responded to letter strings which subtended a horizontal visual angle of 3.95 deg, while a second group responded to strings which subtended 1.02 deg. Correct identifications of critical letters showed that the presentation of words resulted in superior performance. This 'word superiority effect' is consistent with earlier findings implying that it has a perceptual locus. For the stimuli which subtended the large visual angle the word advantage was detrimentally affected only when the position of the critical letter to be identified was cued either 500 or 510 ms prior to the display of the letter string.