The temporal course of startle reflex modulation
and autonomic response patterns to fear-relevant and fear-irrelevant
pictures in subjects with high and low levels of animal
fear was investigated. Thirty-eight high-fear and 48 low-fear
volunteers viewed photos of snakes and spiders and pictures
of neutral and pleasant content. The slides were presented
for 6 s or for only 150 ms, depending on the group. Acoustic
startle probes were presented at five different times after
slide onset. Relative potentiation of the startle responses
started 300 ms after onset of snake/spider pictures in
fearful subjects. This fear-potentiated startle effect
was maintained for the later probe times and was identical
in the 150-ms condition. Fear-relevant pictures also prompted
a sympathetically dominated autonomic response profile
in fearful persons. These data support the idea that fear
can be activated very rapidly, requiring only minimal stimulus
input.