Inattentional blindness
Inattentional blindness or perceptual blindness occurs when an individual fails to perceive an unexpected stimulus in plain sight, purely as a result of a lack of attention rather than any vision defects or deficits. When it becomes impossible to attend to all the stimuli in a given situation, a temporary "blindness" effect can occur, as individuals fail to see unexpected but often salient objects or stimuli.
The term was chosen by Arien Mack and Irvin Rock in 1992 and was used as the title of their book of the same name, published by MIT Press in 1998, in which they describe the discovery of the phenomenon and include a collection of procedures used in describing it. A famous study that demonstrated inattentional blindness asked participants whether or not they noticed a person in a gorilla costume walking through the scene of a visual task they had been given.
Research on inattentional blindness suggests that the phenomenon can occur in any individual, independent of cognitive deficits. However, recent evidence shows that patients with attention deficit hyperactivity disorder performed better attentionally when engaging in inattentional blindness tasks than control patients did, suggesting that some types of neuro-divergence may decrease the effects of this phenomenon. Recent studies have also looked at age differences and inattentional blindness scores, and results show that the effect increases as humans age. There is mixed evidence that consequential unexpected objects are noticed more: Some studies suggest that humans can detect threatening unexpected stimuli more easily than nonthreatening ones, but other studies suggest that this is not the case. There is some evidence that objects associated with reward are noticed more.
Numerous experiments and art works have demonstrated that inattentional blindness also has an effect on people's perception.
Defining criteria
The following criteria are required to classify an event as an inattentional blindness episode: 1) the observer must fail to notice a visual object or event, 2) the object or event must be fully visible, 3) observers must be able to readily identify the object if they are consciously perceiving it, and 4) the event must be unexpected and the failure to see the object or event must be due to the engagement of attention on other aspects of the visual scene and not due to aspects of the visual stimulus itself. Individuals who experience inattentional blindness are usually unaware of this effect, which can play a subsequent role on behavior.Inattentional blindness is related to but distinct from other failures of visual awareness such as change blindness, repetition blindness, visual masking, and attentional blink. The key aspect of inattentional blindness which makes it distinct from other failures in awareness rests on the fact that the undetected stimulus is unexpected. It is the unexpected nature of said stimulus that differentiates inattentional blindness from failures of awareness such as attentional failures like the aforementioned attentional blink. It is critical to acknowledge that occurrences of inattentional blindness are attributed to the failure to consciously attend to an item in the visual field as opposed the absence of cognitive processing.
Findings such as inattentional blindness – the failure to notice a fully visible but unexpected object because attention was engaged on another task, event, or object – has changed views on how the brain stores and integrates visual information, and has led to further questioning and investigation of the brain and importantly of cognitive processes.
Cognitive capture
Cognitive capture or, cognitive tunneling, is an inattentional blindness phenomenon in which the observer is too focused on instrumentation, task at hand, internal thought, etc. and not on the present environment. For example, while driving, a driver focused on the speedometer and not on the road is suffering from cognitive capture.Early vs. late selection of attention
One of the foremost conflicts among researchers of inattentional blindness surrounds the processing of unattended stimuli. More specifically, there is disagreement in the literature about exactly how much processing of a visual scene is completed before selection dictates which stimuli will be consciously perceived, and which will not be. Two basic schools of thought exist on the issue – those who believe selection occurs early in the perceptual process, and those who believe it occurs only after significant processing. Early selection theorists propose that perception of stimuli is a limited process requiring selection to proceed. This suggests that the decision to attend to specific stimuli occurs early in processing, soon after the rudimentary study of physical features; only those selected stimuli are then fully processed. On the other hand, proponents of late selection theories argue that perception is an unlimited operation, and all stimuli in a visual scene are processed simultaneously. In this case, selection of relevant information is done after full processing of all stimuli.While early research on the topic was heavily focused on early selection, research since the late 1970s has been shifted mainly to the late selection theories. This change resulted primarily from a shift in paradigms used to study inattentional blindness which revealed new aspects of the phenomenon. Today, late selection theories are generally accepted, and continue to be the focus of the majority of research concerning inattentional blindness.
Kagen
Evidence for late selection
A significant body of research has been gathered in support of late selection in the perception of visual stimuli.One of the popular ways of investigating late selection is to assess the priming properties of unattended stimuli. Often used to demonstrate such effects is the stem completion task. While there exist a few variations, these studies generally consist of showing participants the first few letters of words, and asking them to complete the string of letters to form an English word. It has been demonstrated that observers are significantly more likely to complete word fragments with the unattended stimuli presented in a trial than with another similar word. This effect holds when stimuli are not words, but instead objects. When photos of objects are shown too quickly for participants to identify, subsequent presentation of those items lead to significantly faster identification in comparison to novel objects.
A notable study by Mack and Rock has also revealed that showing a word stimulus differing from the participant's name by one letter did not generally call conscious attention. By simply changing a character, transforming the presented word into the observer's first name, the now highly meaningful stimulus is significantly more likely to be attended to. This suggests that the stimuli are being extensively processed, at least enough to analyze their meaning. These results point to the fact that attentional selection may be determined late in processing.
The evidence outlined above suggests that even when stimuli are not processed to the level of conscious attention, they are nonetheless perceptually and cognitively processed, and can indeed exert effects on subsequent behavior.
Evidence for early selection
While the evidence supporting late selection hypotheses is significant and has been consistently reproduced, there also exists a body of research suggesting that unattended stimuli in fact may not receive significant processing.For example, in a functional magnetic resonance imaging study by Rees and colleagues, brain activity was recorded while participants completed a perceptual task. Here they examined the neural processing of meaningful and meaningless stimuli both when attended to, and when these same items were unattended. While no difference in activation patterns were found between the groups when the stimuli were unattended, differences in neural processing were observed for meaningful versus meaningless stimuli to which participants overtly attended. This pattern of results suggests that ignored stimuli are not processed to the level of meaning, i.e. less extensively than attended stimuli. Participants do not seem to be detecting meaning in stimuli to which they are not consciously attending.
Some visual input information is only available in the primary visual cortex and not visible to visual awareness. One such information is regarding which eye sees which visual inputs. However, this information has been observed to guide attentional or gaze shifts, indicating a selection at the very first stage when visual inputs enter visual cortex. This information about the eye of origin of visual inputs is then deleted by V2, right after V1 along the visual pathway, since V2 neurons' responses to visual inputs do not depend on from which eye the visual inputs come from.
Theories
Perceptual load
This particular hypothesis bridges the gap between the early and late selection theories. Authors integrate the viewpoint of early selection stating that perception is a limited process, and that of the late selection theories assuming perception as an automatic process. This view proposes that the level of processing which occurs for any one stimulus is dependent on the current perceptual load. That is, if the current task is attentionally demanding and its processing exhausts all the available resources, little remains available to process other non-target stimuli in the visual field. Alternatively, if processing requires a small amount of attentional resources, perceptual load is low and attention is inescapably directed to the non-target stimuli.The effects of perceptual load on the occurrence of inattentional blindness is demonstrated in a study by Fougnie and Marois. Here, participants were asked to complete a memory task involving either the simple maintenance of verbal stimuli, or the rearrangement of this material, a more cognitively demanding exercise. While subjects were completing the assigned task, an unexpected visual stimulus was presented. Results revealed that unexpected stimuli were more likely to be missed during manipulation of information than in the more simple rehearsal task.
In a similar type of study, fMRI recordings were done while subjects took part in either low-demand or high-demand subtraction tasks. While performing these exercises, novel visual distractors were presented. When task demands were low and used a smaller portion of the finite resources, distractors captured attention and sparked visual analysis as shown by brain activation in the primary visual cortex. These results, however, did not hold when perceptual load was high; in this condition, distractors were significantly less often attended to and processed.
Thus, higher perceptual load, and therefore more significant use of attentional resources, appears to increase the likelihood of inattentional blindness episodes.