Seven experiments explore the role of bottlenecks in selective attention and access to visual shortterm memory in the failure of observers to identify clearly visible changes in otherwise stable visual displays. Experiment One shows that observers fail to register a color change in an object even if they are cued to the location of the object by a transient at that location as the change is occurring. Experiment Two shows the same for orientation change. In Experiments Three and Four, attention is directed to specific objects prior to making changes in those objects. Observers have only a very limited memory for the status of recently attended items. Experiment Five reveals that observers have no ability to detect changes that happen after attention has been directed to an object and before attention returns to that object. In Experiment Six, attention is cued at rates that more closely resemble natural rates and Experiment Seven uses natural images. Memory capacity remains very small (<4 items).If you ask typical observers, outside of a vision research laboratory, what they are seeing right now, they will probably tell you that they are seeing a large number of objects placed in a spatially continuous scene. If you ask them if they are seeing all of that at the same time, they will look at you quizzically but they will agree that all of the objects seem to be visually present in the present instant of time. It hardly seems like much of a question. However, if you ask atypical observers, those who have been studying the question over the past 20 years or so, the answers may be quite different. A range of phenomena suggest that human observers are unable to perform tasks that would seem to be quite trivial if we could see what was in front of our eyes in the uncomplicated manner suggested by naïve introspection.Change blindness is one of the most striking of these phenomena. In a typical change blindness paradigm, the observer is told to monitor an image for a change. As long as transients are masked and as long as the observer is not attending to the object that is changing, observers will be very poor at detecting quite substantial changes. These can range from changes to significant objects in natural scenes to changes in "basic features" like color (Phillips, 1974;Rensink, O'Regan, & Clark, 1997;Simons, 2000;Simons & Levin, 1997).Similar failures to report what is in front of the eyes occur when observers are attending to one aspect of a display and subsequently queried about another. Thus, Mack and Rock (1998) found that observers who were answering a question about a pair of lines would fail to report salient stimuli presented at fixation ("inattentional blindness"). Simons Neisser & Becklen, 1975) have shown that observers who were monitoring one set of actors would fail to notice other actors (e.g. a woman in a gorilla suit) as they entered and left a scene (Simons & Chabris, 1999).Some have argued that these results demonstrate that we only "see" the current object of attention and that the re...

In an array of elements whose colors vary can we selectively choose to process all the items of a particular color preferentially in relation to those of another color? We addressed this question by presenting subjects with arrays containing many elements, and recording reaction times to a luminance change of one of the elements. Half the elements had one color and the other half another color--the spatial distribution being random. In two tasks--a simple detection of this change or a choice reaction time to the polarity of the change--we found that reaction times were independent of the number of items in the array. Cuing the subjects as to the color of the target item had no significant influence on the detection task, but subjects were faster if cued for the discrimination task. A further experiment replicated these findings and examined possible costs and benefits. Our final experiment separated the roles of attentional guidance and postattentional processes by having subjects judge the orientation of the target element and varying the magnitude of the target flash that defined which element was the target. We found that this judgment was also affected by color cuing, and that the size of the effect interacted with the flash strength, suggesting that color cuing has its influence at the stage of attentional guidance. We conclude that subjects can selectively attend to items on the basis of color given the appropriate task and stimulus dynamics.

Selective attention to 1 of 2 overlapping objects was assessed in a cuing paradigm. Participants detected or identified targets that appeared in 1 of 6 possible target locations (3 on each object). Significant cuing effects for the simple detection of such targets using both reaction time and sensitivity measures of performance were found. Cuing effects were consistently greater when the participants were required to identify some aspect of the target even when the tasks (detection vs. identification) were equated for overall performance level. These differences in cuing effects between tasks were much reduced if the target locations were no longer grouped into 2 objects. It is suggested that identical stimuli can elicit differing attentional mechanisms depending on task type (rather than task difficulty) and that these mechanisms differ in the nature of the representation of the visual world. A flash of lightning by night, the report of a firearm, the sudden prick of a knife, or a violent internal pain, all these for the moment so occupy our notice that everything else becomes feeble or is banished. (Bradley, 1886, p. 306) Bradley's (1886) quote summarizes people's introspection that when they are attending to one thing, they become less aware of other things. Modern experimental psychologists have devoted much work to defining the details of this general statement. However, there are still fundamental issues that have yet to be resolved. In this article we attempt to address some of them: What constitutes the "thing" of people's attention (an area of space or an object)? Are all tasks affected by attention, and, if so, are they affected equally? Are there differences in attending to something by a deliberate act of will versus when this something automatically draws attention to itself?. To what extent does the difficulty of the task act to determine the effects of attention? Such questions have importance not only in producing theoretical accounts of attentional processes but also for their practical implications. For instance, there is an increasing use of head-up displays (HUDs) in both aviation and driving situations (Sojourner & Antin, 1990; Tufano, 1997; Weintraub & Ensing, 1992; Wickens & Long, 1995). HUDs attempt to overlay information relevant to the user onto the image received from the outside world. The hope is that the two images will fall onto the same parts of the retina and thus time might be saved in switching gaze and accommodation between the two images. However, it might be that

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Many visual tasks have been shown to be influenced by the attentional state of the observer. However the conditions under which attention has effects is still unclear. Here we report upon a series of experiments where the observer has to react to changes in the luminance of a target amongst many distractors. We have systematically manipulated the nature of the cue (endogenous vs exogenous) and the task to be performed (detection of changes vs discrimination of direction of change). Stimuli consisted of a number of circles upon a screen. At some point in time one of the circles changed in luminance and subjects reacted as quickly as possible. Typically half the circles were red and half green. Subjects could be cued to attend to a particular colour by instruction (endogenous) or by a brief flash of the lines that joined the same coloured elements (exogenous). In most cases the cue was appropriate on 80% of the trials and hence we could compare response times between valid and invalid trials. Our results show that (1) for simple detection endogenous cues were ineffective whereas exogenous cues provided a small advantage for the valid trials, and (2) for discrimination of direction of change endogenous cues provided a small advantage, whereas exogenous cues provided a large advantage for the valid trials. It appears that both cueing type and task type modulate the attentional effects on this ‘preattentive’ task.