Prepulse inhibition (PPI) with 22 lux (A) and 100 lux (B) visual prepulses conducted at 2 months of age. A significant condition × interstimulus interval (ISI) interaction was detected, indicating that the HIV-1 Tg group was less sensitive to the manipulation of ISI, as illustrated by their flatter ISI functions. Percent PPI at the point of peak inhibition: 1 light: HIV-1-Tg, 74.9%±2.5; Control, 72.2%±2.6; 2 lights: HIV-1-Tg, 66.3%±3.8; Control, 73.9%±3.1.