Effects of relative position and shape relation on gap detection with geometric form pairs.

A letter presented parafoveally is better identified when flanked by a letter to its foveal side than when flanked by a letter to its peripheral side if the letters are different in shape. If the letters are similar, relative position does not affect identifiability. Whereas some articles in the literature suggest that this effect may not extend to geometric forms, results of the first experiment showed that it does. Results of the second experiment revealed that the strength of the significant interaction between relative position and shape relation remains constant over a range of eccentricities (2-20 deg were tested) extending above and below as well as to the left and right of fixation. Results are compared with predictions from a model that can account for the relative position-shape relation interaction.