Selective attention, visual awareness and the attentional blink

The research reported in this thesis dealt with the attentional blink: a phenomenon that provides a window into the temporal and functional architecture of the processes mediating the selection and transfer of visual information into awareness. The main empirical hallmark of the attentional blink is the finding of an impairment in responses to the second of two stimuli presented briefly and within half a second of each other. The types of stimuli and tasks across which such impairments have been found to occur are diverse. For example, an attentional blink can be triggered by making a speeded pitch discrimination response to a low or a high pitched beep (Jolicoeur, 1999) and it can impair performance on tasks as simple as detecting a pop-out search target (Joseph, Chun & Nakayama, 1997). One of the main goals of the research summarized in this chapter was to challenge the inevitability of the impairment in report of the second target presented during the attentional blink. To this end, different manipulations were applied to tasks requiring report of two masked, visual targets, in an attempt to facilitate the transfer of T2 to visual awareness. In summary, the present research revealed the following characteristics of the processes involved in selecting and consolidating visual stimuli that are presented in rapid succession. First, an attentional blink is triggered when a masked stimulus that attracts attention either because it has to be identified or because it cannot be ignored and therefore produces contingent attentional capture (see Chapter 4). This is evidenced by a marked impairment in the identification of second targets presented within a period of approximately 500 ms after the presentation of this first stimulus. The impairment in second target identification can be attenuated or even fully prevented by precuing the arrival of the second target with an item that matches the target specification for T2 (Chapters 2 and 3). Whether or not a precuing manipulation will produce full recovery or only attenuation of the impairment in T2 report may depend on the temporal interval separating the onset of the cue and that of the target. Effective precues are items that match the visual characteristics of the targets, whereas categorical precues and memorized distractor precues do not produce enhanced report of T2. The attentional blink does not affect the ability to reorient the focus of spatial attention to a location different than the one where the first target was presented. In particular, similar impairments in second target report are observed regardless of whether this target is presented at the same or at a different location than the first target (Chapter 4). RSVP targets are not more likely to be reported when they are held in memory (Chapter 5). Instead, surprisingly, report of these targets was found to impaired relative to report of non-memorized targets