Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

Researchers have developed clever ways to peek over the mind’s shoulder and track brain activity lying beneath the level of conscious awareness. Some of the most striking studies involve patients who have lost some degree of neurological function. A well-known case, involving a subject known as P.S. who sustained right cerebral damage, was documented in the late 1980s by Peter Halligan and John Marshall.11 As anticipated with this type of impairment, P.S. would fail to report details on the far left side of any image she was shown. She claimed, for instance, that two dark green line drawings of a house were identical even though the left side of one of the houses was being consumed by a raging red fire. Yet, when asked which of the two houses she’d prefer to call home, P.S. consistently chose the house that was not burning. The researchers argued that although P.S. was unable to acquire conscious awareness of the blaze, the information had entered covertly and was influencing her decision from behind the scenes. Healthy brains, too, reveal their own dependence on hidden influences. Psychologists have established that even if you are paying close attention, an image flashed on-screen for less than about forty milliseconds (and sandwiched between somewhat longer flashes of other images known as masks) will fail to enter your conscious awareness. Nevertheless, such subliminal images can influence conscious decisions.