Sustained inattentional blindness: What you see is what you set

When people are engaged in an attentionally demanding task, they often fail to notice unexpected objects appearing right in front of them. This is a phenomenon known as inattentional blindness. Despite the ubiquity of inattentional blindness in everyday life, little is known about the factors that determine whether or not a person will perceive an unexpected object. My dissertation research attempts to remedy this situation, and it addresses several overarching questions. (1) Do some stimulus features, such as salience or abrupt onset, grab hold of awareness such that they are noticed almost all the time? (2) How much of what we notice is contingent on how we "tune" our attention? (3) Given prior evidence that attention might be drawn automatically, can visual awareness be dissociated from such automatic orienting? (4) If attentional orienting to visual stimuli can be dissociated from visual awareness of them, what might be the functional relationship between them, if any? Together with my colleagues, I developed a highly controlled sustained inattentional blindness task in order to explore these issues. Subjects selectively attended to one of two sets of items moving on a computer display during several trials. On a critical trial, a new object unexpectedly entered the display, crossed behind a fixation point, and exited the opposite side, remaining visible for 5 seconds. Subjects were then probed to determine whether they had been aware of the unexpected object. In three papers, I explored the contributions of both stimulus-based properties and top-down attentional tuning to the likelihood that subjects would notice unexpected objects. Some bottom-up stimulus characteristics, such as salience and spatial location, did increase noticing rates, but none guaranteed that subjects would notice the unexpected object. Rather, subjects' feature-based attentional set appeared to wield the strongest influence. In addition, attentional distraction caused by the unexpected object occurred even when the object was undetected. Thus, implicit shifts of attention might be dissociable from awareness. A potential functional relationship between implicit attention shifts and awareness is discussed.