How to differentiate between neglect and hemianopia. Four experiments on healthy subjects

One of the most frequent difficulty in neuropsychological assessment is the differentiation between neglect and hemianopia. Since there is a wide agreement in implicit information processing for patients with neglect, we hypothesized that a priming word in the neglected field should determine a semantic activation effect even when it is not consciously perceived by the patient. On the contrary if the priming word occurs in a blind hemifield this should not determine any facilitation effect. As first step we tested a “locally-dependent” priming effect on healthy subjects in a semantic categorization task. We conducted four experiments in which we modulated the presence of a string of “X” contralaterally to prime position, prime duration (150 vs 300 ms) and distance from monitor (50 cm vs 100 cm). Prime occurred in six different positions while target appeared in the center of the screen. Three different prime-target conditions were present: related, unrelated and neutral. Twenty healthy subjects took part to the first experiment (prime at 150 ms, 50 cm from monitor); 17 to the second (prime at 150 ms without contralateral string of X, 50 cm distance); 15 to the third (prime at 300 ms, 50 cm from monitor) and 17 to the fourth (prime at 300 ms, 100 cm from monitor). Results: we obtained a significant main effect of semantic relation (p < .001) in all experiments but not in the first one. We then found a significant main effect of position (p < .05); in the fourth experiment (prime at 300 ms) this was significant for all the positions of the prime (p = .001). Moreover we observed that priming duration significantly affects subjects’ performance with slower RTs. No significances arose between the two distances from monitor. These first results confirmed significant semantic activation effect for different prime positions, specifically a higher prime duration seems to provide a more sensitive task to be used as differential between neglect and hemianopia