There was very little change blindness provided observers’ attention was directed to the rectangle that might change within 900 ms of the offset of the first array. Landman et al. (2003) concluded we can have access to fairly detailed information about the current visual scene for almost 1 second. However, it is important that what we currently perceive is not disrupted by what we perceive next. Such disruption occurs when there is overwriting of the previous scene with the current one. A consequence of such overwriting is that we often exhibit change blindness.
Busch et al. (2009) argued that we should distinguish two types of change detection: (1) sensing there has been a change without conscious awareness of which object has changed; and (2) seeing the object that has changed. Busch et al. used event-related potentials (ERPs; see Glossary). ERP components associated with selective attention and conscious processing of visual changes were associated with seeing but not sensing. Much research is problematical due to a failure to distinguish clearly between sensing and seeing.
Howe and Webb (2014) argued that sensing often occurs when observers detect a global change in a visual scene. Observers were presented with an array of 30 discs (15 red, 15 green). On some trials, three discs all the same colour changed from red to green or vice versa. On 24% of trials, observers detected the array had changed without being able to identify any of the discs that had changed. Thus, there was frequently sensing of global change without seeing which objects had changed.
Finally, Fischer and Whitney (2014) proposed a new theoretical approach that may well enhance understanding of change blindness. They argued that perceptual accuracy is sacrificed to some extent so that we can have continuous, stable perception of our visual environment. Observers reported the perceived orientation of black-and-white gratings presented several seconds apart. The key finding was that the perceived orientation of a grating was biased in the direction of the previous grating even when it had been presented ten seconds earlier. The visual system’s emphasis on perceptual stability may inhibit our ability to detect changes within the visual scene.
Figure 4.14
The sequence of events in the disappearing lighter trick: (a) the magician picks up a lighter with his left hand and (b) lights it; (c) and (d) he pretends to take the flame with his right hand and (e) gradually moves it away from the hand holding the lighter; (f) he reveals his right hand is empty while the lighter is dropped into his lap; (g) the magician directs his gaze to his left hand and (h) reveals that his left hand is also empty and the lighter has disappeared.
From Kuhn and Findlay (2010). Reprinted with permission of Taylor & Francis.
Many studies (including Kuhn & Findlay, 2010) show the role of inattentional blindness caused by misdirection in magic tricks (Kuhn & Martinez, 2012). However, there is an important difference between misdirection and inattentional blindness as typically studied (Kuhn & Tatler, 2011). Most studies on inattentional blindness (e.g., Simons & Chabris, 1999) require a distractor task to reduce the probability observers will detect the novel object. Misdirection research is more impressive and realistic in that no explicit distractor is needed to produce inattentional blindness.
Smith et al. (2012) studied change blindness using a magic trick in which a coin was passed from one hand to another and then dropped on the table. The participants’ task was to guess whether the coin would land with heads or tails facing up (see online at http://dx.doi.org/10.1068/p7092). The coin was switched during a critical trial from a UK 1p to 2p, 50p to old 10p or US quarter to Kennedy half dollar. All participants fixated the coin throughout the entire time it was visible, but 88% or more failed to detect the coin had changed! Thus, change blindness can occur even though the crucial object is fixated. More specifically, an object can be attended to without some of the features irrelevant to the current task being processed thoroughly.
Figure 4.15
Participants’ fixation points at the time of dropping the lighter for those detecting the drop (triangles) and those missing the drop (circles).
From Kuhn and Findlay (2010). Reprinted with permission of Taylor & Francis.
Weblink:
Magical videos
1 the similarity of the unexpected object to task-relevant stimuli;
2 the observer’s available processing resources.
Earlier we discussed the surprising finding (Simons & Chabris, 1999) that 50% of observers failed to detect a woman dressed as a gorilla. Similarity (or rather dissimilarity) was a factor in that the gorilla was black, whereas the team members whose passes the observers counted were dressed in white.
Simons and Chabris carried out a further experiment in which observers counted the passes made by members of the team dressed in white or the one dressed in black.
What did Simons and Chabris (1999) find? The gorilla’s presence was detected by only 42% of observers when the attended team was the one dressed in white, thus replicating the previous findings. However, the gorilla’s presence was detected by 83% of observers when the attended team was the one dressed in black. This shows the importance of similarity between the unexpected stimulus (gorilla) and task-relevant stimuli (members of attended team).
Figure 4.16
Percentage of participants detecting an unexpected object. When it was an E, more participants detected when they were attending to letters than when attending to numbers. The opposite was the case when the unexpected object resembled block-like 3.
From Most (2013). © 2011 Springer-Verlag. Reprinted with permission of the publisher.
Simons and Chabris’s (1999) findings indicate the importance of similarity in stimulus features (e.g., colour) between task stimuli and the unexpected object. Most (2013) argued that similarity in terms of semantic category was also important. Participants tracked numbers (2, 4, 7, 9) or letters (A, H, L, U).
On the critical trial, an unexpected stimulus (the letter E or number 3) was visible for seven seconds. Of key importance, the letter and number were visually identical except that they were mirror images of each other. What was of interest was the percentage of observers who noticed the unexpected object.
What did Most (2013) find? There was much less inattentional blindness when the unexpected object belonged to the same category as the tracked objects (see Figure 4.16). Thus, inattentional blindness can depend on attentional sets based on semantic categories (e.g., letters, numbers).
Richards et al. (2012) studied the effects of working memory capacity (related to availability of processing resources and attentional control; see Glossary) on inattentional blindness. Individuals high in working memory capacity were less likely than low scorers to exhibit inattentional blindness.
The findings of Richards et al. (2012) suggest inattentional blindness occurs due to insufficient attentional resources. However, that is not the whole story. Eitam et al. (2013) presented observers with very simple stimuli: a coloured circle surrounded by a differently coloured ring. Performance was close to perfect when the observers tried to identify both colours, indicating they had the processing resources to attend to both stimuli. However, the findings were very different when they were instructed to focus on only the circle or ring. In this condition, there was clear evidence of inattentional blindness with 20% of observers failing to identify the task-irrelevant colour. Thus, inattentional blindness can depend more on attentional set than availability of processing resources.
Evaluation
Change blindness and inattentional blindness are important phenomena occurring in everyday life (e.g., the movies, magic tricks). Most research indicates attentional processes are important, but finer distinctions (e.g., between overt and covert attention) are also needed. Research has increasingly identified various ways change blindness can occur, including a failure to compare the pre- and post-change object representations. Inattentional blindness is mainly due to attentional sets reducing processing of task-irrelevant stimuli not included within the set.
What are the limitations of research in this area? First, there has been a general failure to distinguish between change detection that involves seeing the change and change detection that involves only sensing a change.
Second, five processes are required for change detection involving seeing to occur and so failure of any of these processes should lead to change blindness. As yet, however, only a few studies (e.g., Varakin et al., 2007) have attempted to distinguish clearly among these potential reasons for change blindness.
CHAPTER SUMMARY
• Introduction. The time dimension is of crucial importance in visual perception. The changes in visual information produced as we move around the environment and/or environmental objects move promote accurate perception and facilitate appropriate actions.
• Direct perception. Gibson argued that perception and action are closely intertwined. According to his direct theory, movement of an observer creates optic flow, which provides useful information about the direction of heading. Invariants, which remain the same as people move around their environment, are of particular importance. The uses of objects (their affordances) were claimed to be perceived directly. Gibson underestimated the complexity of visual processing and object recognition, and he oversimplified the effects of motion on perception.
• Visually guided action. Perception of heading depends in part on optic-flow information. However, there are complexities because the retinal flow field is determined by eye and head movements as well as by optic flow. Heading judgements are also influenced by binocular disparity and the retinal displacement of objects as we approach them.
Accurate steering on curved paths (e.g., driving around a bend) sometimes involves focusing on the tangent point (e.g., point on the inside edge of the road at which its direction seems to reverse). However, it often involves fixating a point along the future path.
Calculating time to contact with an object sometimes seems to depend on tau (the size of the retinal image divided by the object’s rate of expansion). However, tau only provides accurate information when moving objects have constant velocity. Observers often make use of additional sources of information (e.g., binocular disparity, familiar size, relative size) when working out time to contact.
• Planning–control model. The planning–control model distinguishes between a slow planning system used mostly before the initiation of movement and a fast control system used during movement execution. According to the model, planning is associated with the inferior parietal lobe, whereas control depends on the superior parietal lobe. The definition of “planning” is very broad, and the notion that planning always precedes control is oversimplified. There are several exceptions to the theoretical expectation that actions based on control will be more accurate than those based on planning.
• Perception of human motion. Human motion is perceived even when only impoverished visual information is available. Perception of human and biological motion involves bottom-up and top-down processes, with the latter most likely to be used with degraded visual input. The perception of human motion is special because we can produce as well as perceive human actions and because we devote considerable time to making sense of it. It has often been assumed that our ability to imitate and understand human motion depends on a mirror neuron system, including brain areas such as inferior frontal regions, the dorsal and ventral premotor cortex, and the inferior and superior parietal lobule. The mirror neuron system is important. However, exaggerated claims have been made concerning its role in human motion perception.
• Change blindness. There is convincing evidence for the phenomena of inattentional blindness and change blindness. Attention (covert and overt) is the single most important factor determining whether inattentional and change blindness occur. Inattentional blindness is especially likely to be found when the unexpected object is dissimilar to task stimuli. Five different processes are required for change detection and failure of any of these processes can cause change blindness. There is an important distinction between seeing a changed object and sensing that some change has occurred. The visual system’s emphasis on continuous, stable perception probably plays a part in making us susceptible to change blindness.
Further reading
• Bruce, V. & Tadmor, Y. (2015, in press). Direct perception: Beyond Gibson’s (1950) direct perception. In M.W. Eysenck & D. Groome (eds), Cognitive psychology: Revisiting the classic studies. London: SAGE. Gibson’s approach to visual perception and action is evaluated in detail by Vicki Bruce and Yoav Tadmor.
• Cook, R., Bird, G., Catmur, C., Press, C. & Heyes, C. (2014). Mirror neurons: From origin to function. Behavioral and Brain Sciences, 37: 177–241.
Richard Cook and his colleagues discuss the probable function or functions of the mirror neuron system.
• Glover, S., Wall, M.B. & Smith, A.T. (2012). Distinct cortical networks support the planning and online control of reaching-to-grasp in humans.
European Journal of Neuroscience, 35: 909–15. Scott Glover and his colleagues provide an update on his planning–control model.
• Jensen, M.S., Yao, R., Street, W.N. & Simons, D.J. (2011). Change blindness and inattentional blindness. Wiley Interdisciplinary Reviews: Cognitive Science, 2: 529–46. The similarities and differences between change blindness and inattentional blindness are discussed thoroughly in this article.
• Lee, D.N. (2009). General tau theory: Evolution to date. Perception, 38: 837–50. David Lee discusses his theoretical approach to perception of motion that developed from Gibson’s theorising.
• Rensink, R.A. (2013). Perception and attention. In D. Reisberg (ed.), The Oxford handbook of cognitive psychology. Oxford: Oxford University Press.
The relationship between perception and attention (including change blindness and inattentional blindness) is discussed at length by Ronald Rensink.
• Shiffrar, M. & Thomas, J.P. (2013). Beyond the scientific objectification of the human body: Differentiated analyses of human motion and object motion. In M. Rutherford and V. Kuhlmeier (eds), Social perception: Detection and interpretation of animacy, agency, and intention. Cambridge, MA:
MIT Press/Bradford Books. This chapter provides an overview of what is known about the perception of biological motion.