Figure 4. Experimental Controls for RT across SAT.
(A) RT and error rate for missed deadlines (premature Accurate and late Fast responses). Mean RT was necessarily reversed (monkey Q t24 = −5.9, p < 0.001; monkey S t14 = −13.2, p < 0.001, two-tailed t tests), but error rate remained greater in the Fast condition (monkey Q t24 = −7.6, p < 0.001; monkey S t14 = −10.9, p < 0.001, two-tailed t tests).
(B) Average normalized activity for all visual salience neurons when the target (solid) or distractors (dashed) appeared in the RF on premature Accurate and late Fast trials (Neutral condition data are not included because there were no deadlines). Despite the reversal of RT, enhanced activity persisted 100–125 ms postarray onset in Fast compared to Accurate trials (t144 = −2.8, p < 0.01, two-tailed t test). Activity in a later period (250–300 ms) was not significantly different (p > 0.05). However, target selection time (vertical arrows) was significantly slower in late Fast (241 ms) than premature Accurate (157 ms) trials (jackknife test t144 = −2,923.2, p < 0.001).
(C) Average normalized activity for all movement neurons when the target appeared in the movement field on premature Accurate and late Fast trials. Even with the reversal of RT, movement activity 20–10 ms before saccade remained higher in late Fast than in premature Accurate trials (t13 = −2.0, p = 0.06, two-tailed t test).
(D) Average normalized activity for all visual salience neurons when the target appeared in the RF on Accurate, Neutral, and Fast trials equated for RT. RTs were equated by constructing a range of RTs based on ±1 SD of the median RT in the Neutral condition. RTs in Accurate, Neutral, and Fast conditions falling outside of this range were excluded, which resulted in low variability between the conditions (e.g., before correction: 614 [Accurate] – 271 [Fast] = 343 ms; after correction: 315 – 269 = 46 ms). Visual salience activity remained elevated in Fast versus Accurate trials 250–300 ms postarray onset (t45 = 4.8, p < 0.001, linear regression) but not in the interval 100–125 ms postarray onset (t45 = 1.7, p = 0.10, linear regression).
(E) Average normalized activity for all movement neurons when the target appeared in the movement field on Accurate, Neutral, and Fast trials equated for RT. Movement activity in the interval 20–10 ms prior to saccade increased with speed stress (t29 = 3.1, p < 0.01, linear regression). Vertical bars in all panels represent ±1 SE drawn at the interval of statistical analysis.