The Time Course Of Phasic Alerting Induced By Invisible Threatening Signals

Alerting refers to the ability of organisms to alter the internal state of arousal and increase response readiness to an imminent stimulus,enabling organisms to respond quickly to environmental events for survival.Unconscious alerting has been confirmed by studies showing that high-frequency flicker stimuli can produce an alerting effect despite the inability to enter the conscious state.In addition,organisms have evolved so as to be very sensitive to threatening stimuli such as spiders and venomous snakes.An interesting question is,for the unconscious alerting effect induced by ecologically important threat-related stimuli compared to that induced by neutral non-threatening stimuli,what are the temporal characteristics and the magnitude of it? In this study,a high-frequency luminance flicker technique was used to make the alerting signal invisible and inaccessible to consciousness,and to explore the differences in the time course and magnitude of the unconscious alerting effects elicited by invisible spiders(high-threatening signal),butterflies(low-threatening signal)and leaves(neutral nonthreatenng signal).In experiment 1,we compared the unconscious alerting effects elicited by invisible spiders and invisible leaves.Results showed that both were able to elicit alerting effects in the unconscious state,with significant differences between their time courses,i.e.the alerting effect of the invisible spiders(high threatening)appeared only in the early stage(SOA 250ms),whereas the alerting effect of the invisible leaves(neutral,nonthreatening)appeared only in the late stage(SOA 750ms).However,there may be an alternative explanation.Given that spiders are animals whereas leaves are plants,the above-mentioned differences in the time course of the alerting effects may simply be due to the introduction of an irrelevant variable,i.e.the biological category of the stimulus.Experiments 2 and 3 were therefore conducted.The unconscious alerting effect induced by invisible spiders was compared to that induced by invisible butterflies in Experiment 2,and the unconscious alerting effect induced by invisible butterflies was compared to that induced by invisible leaves in Experiment 3.If the difference in the time course of the unconscious alerting effect in Experiment 1 was due to threatening information,the results in Experiment 2 was expected to be similar to that in Experiment 1.By contrast,if the results found in Experiment 1 were due to the difference in the biological category between spiders and leaves,the results in Experiment 3 was expected to be similar to that in Experiment 1.In Experiment 2,we found that the alerting effect for invisible spiders(high threatening signal)occurred only at the early stage(SOA 250ms)and the alerting effect for invisible butterflies(low threatening signal)occurred only at the late stage(SOA 750ms),highly similar to the results found in Experiment 1.By contrast,in Experiment 3,we found that the alerting effect of both the invisible butterflies and invisible leaves occurred only at the late stage(SOA 750ms).In summary,the time course of unconscious alerting elicited by high-threatening signals is different from that elicited by low-threatening or neutral non-threatening signals.Our findings suggested that there might be two different mechanisms responsible for unconscious alertness: One is a general cortical mechanism of unconscious alerting elicited by non-threatening or low-threatening signals,another is a subcortical mechanism,which may include subcortical structures,such as the amygdala,and may be responsible for ecologically important high-threatening signals in a rapid and unconscious way.