Research on monkeys in the 1990s led to a new theoretical approach to understanding biological motion. For example, Gallese et al. (1996) assessed brain activity in monkeys in two situations: (1) the monkeys performed a given action (e.g., grasping); and (2) the monkeys observed another monkey perform the same action. Their key finding was that 17% of the neurons in area F5 of the premotor cortex were activated in both situations. They called them
“mirror neurons”.
Findings such as those of Gallese et al. (1996) led theorists to propose a mirror neuron system. This mirror neuron system consists of neurons activated when an animal performs an action and when another animal performs the same action.
KEY TERM
Mirror neuron system
Neurons that respond to actions whether performed by oneself or someone else; it is claimed these neurons assist in imitating and understanding others’ actions.
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Mirror neuron system
This system allegedly facilitates imitation and understanding of the actions of others. The notion of a mirror neuron system has been used to explain aspects of human understanding of speech (see Chapter 9).
The identification of a mirror neuron system in monkeys led to huge interest in finding a similar system in humans. Molenberghs et al. (2012a) reported a meta-analysis (see Glossary) based on 125 human studies. The most important findings were based on “classical” studies in which participants viewed visual images or human actions and/or executed motor actions. The brain regions most associated with the mirror neuron system included the inferior frontal gyrus and inferior parietal lobule (see Figure 4.10). Reassuringly, these brain areas are the human equivalents of the areas most associated with the mirror neuron system in monkeys.
Figure 4.10
Brain areas associated with the mirror neuron system in a meta-analysis of classical studies (defined in text). The brain areas involved included the inferior parietal lobule, the posterior inferior frontal gyrus, the ventral premotor cortex, the dorsal premotor cortex, the superior parietal lobule, the middle temporal gyrus and the cerebellum.
From Molenberghs et al. (2012a). Reprinted with permission of Elsevier.
The studies reviewed by Molenberghs et al. (2012a) show the same brain areas are involved in motion perception and action production. However, we need to show the same neurons are activated whether observing a movement or performing it. This has occasionally been done. Mukamel et al. (2010) identified neurons in various brain areas (e.g., the supplementary motor area) responding to the perception and execution of hand-grasping actions.
Before proceeding, note the term “mirror neuron system” is somewhat misleading. It is typically assumed mirror neurons play a role in working out why someone else is performing certain actions as well as deciding what those actions are. However, mirror neurons do not provide us with an exact motoric coding of observed actions. As Williams (2013, p. 2962) wittily observed, “If only this was the case! I could become an Olympic ice-skater or a concert pianist!”
Findings
Areas within the mirror neuron system are typically activated when someone observes the actions of another person (Cook et al., 2014). However, this is only correlational evidence – it does not show the mirror neuron system is necessary for imitation. Mengotti et al. (2013) considered this issue. They applied transcranial magnetic stimulation (TMS; see Glossary) to areas within the mirror neuron system to disrupt its functioning. As predicted, this impaired participants’ ability to imitate another person’s actions.
Research shows mirror neurons are involved in working out why someone else is performing certain actions. For example, consider a study by Umiltà et al. (2001). They used two main conditions. In one condition, the experimenter’s action directed towards an object was fully visible to the monkey participants. In the other condition, the monkeys saw the same action but the most important part was hidden behind a screen. Before each trial, the monkeys saw the experimenter place some food behind the screen so they knew what the experimenter was reaching for.
What did Umiltà et al. (2001) find? First, over half the mirror neurons tested discharged in the hidden condition. Second, about half of the mirror neurons that discharged in the hidden condition did so as strongly as in the fully visible condition. Third, Umiltà et al. used a third condition that was the same as the hidden condition except the monkeys knew no food had been placed behind the screen. In terms of the experimenter’s actions, this condition was identical to the hidden condition. However, mirror neurons that discharged in the hidden condition did not discharge in this condition. Thus, the meaning of the observed actions determined activity within the mirror neuron system.
Iacoboni et al. (2005) claimed our understanding of the intentions behind someone else’s actions is often helped by taking account of context. For example, someone may shout loudly at another person because they are angry or because they are acting in a play. Iacoboni et al. investigated whether the mirror neuron system in humans was sensitive to context using these two conditions:
1 Intention condition: There were films clips of two scenes involving a teapot, mug, biscuits, a jar and so on – one scene showed the objects before being used (drinking context) and the other showed the object after being used (cleaning context). A hand was shown grasping a cup in a different way in each scene.
2 Action condition: The same grasping actions were shown as in the intention condition. However, the context was not shown, so it was impossible to understand the intention of the person grasping the cup.
There was more activity within the mirror neuron system in the intention than the action condition. This suggests the mirror neuron system is involved in understanding the intentions behind observed actions – it was only in the intention condition that participants could work out why the person was grasping the cup.
Lingnau and Petris (2013) argued that understanding the actions of another person often involves relatively complex cognitive processes as well as simpler processes occurring within the mirror neuron system. They presented two groups of participants with the same point-light displays showing human actions and asked one group to identify the goal of each action. Areas within prefrontal cortex (which is associated with high-level cognitive processes) were more activated when goal identification was required. Understanding another person’s goals from their actions seems to involve more complex cognitive processes than those occurring directly within the mirror neuron system.
Evaluation
Several important findings have emerged from research. First, our ability to perceive human or biological motion with very limited visual information is impressive. Second, the brain areas involved in human motion perception differ somewhat from those involved in perceiving motion in general. Third, perception of human motion is special because it is the only type of motion we can perceive and produce. Fourth, there is some support for the notion of a mirror neuron system allowing us to imitate and understand other people’s movements.
What are the limitations of research in this area? First, much remains to be discovered about the ways bottom-up and top-down processes interact when we perceive biological motion.
Second, some claims for the mirror neuron system are clearly exaggerated. For example, Eagle et al. (2007, p. 131) claimed the mirror neuron system suggests “the automatic, unconscious, and non-inferential simulation in the observer of the actions, emotions, and sensations carried out and expressed by the observed”. In fact, understanding another person’s goals from their actions involves more than these mirror neuron system processes (Lingnau & Petris, 2013). As Csibra (2008, p. 443) argued, it is more likely that “[mirror neurons] reflect action understanding rather than contribute to it”.
Third, it is improbable that the mirror neuron system accounts for all aspects of action understanding. As Gallese and Sinigaglia (2014, p. 200) pointed out, action understanding “involves representing to which … goals the action is directed; identifying which beliefs, desires, and intentions specify reasons explaining why the action happened; and realising how those reasons are linked to the agent and to her action”.
Fourth, the definition of “mirror neurons” is variable. Such neurons respond to the observation and execution of actions. However, there are disagreements as to whether the actions involved must be the same or only broadly similar (Cook et al., 2014).
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Demonstration of change blindness
CHANGE BLINDNESS
We have seen in the chapter so far that a changing visual environment provides valuable information. For example, it allows us to move in the appropriate direction and to make coherent sense of the world around us. In this section, however, we will discover that our perceptual system does not always respond appropriately to changes within the visual environment.
Have a look around you (go on!). We imagine you have a strong impression of seeing a vivid and detailed picture of the visual scene. As a result, you are probably confident you could immediately detect any reasonably large change in the visual environment. In fact, our ability to detect such changes is often far less impressive than that.
Change blindness, which is “the surprising failure to detect a substantial visual change” (Jensen et al., 2011, p. 529), is the main phenomenon we will discuss. We will also consider the related phenomenon of inattentional blindness, which is “the failure to notice an unexpected, but fully-visible item when attention is diverted to other aspects of a display” (Jensen et al., 2011, p. 529).
KEY TERMS
Change blindness
Failure to detect various changes (e.g., in objects) in the visual environment.
Inattentional blindness
Failure to detect an unexpected object appearing in the visual environment.
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Demonstration of inattentional blindness
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Gorillas in the midst
Suppose you watch a video in which students dressed in white pass a ball to each other. At some point, a woman in a black gorilla suit walks into camera shot, looks at the camera, thumps her chest and then walks off (see Figure 4.11). Altogether she is on the screen for nine seconds. You probably feel absolutely certain you would spot the gorilla figure almost immediately. Simons and Chabris (1999) carried out an experiment along the lines just described (see the video at www.simonslab.com/videos.html). Very surprisingly, 50% of the observers totally failed to notice the gorilla! This is a striking example of inattentional blindness.
The original research on inattentional blindness was carried out by Mack and Rock (1998). In their early experiments, observers fixated the intersection point of the two arms of a cross presented for 200 ms and decided which arm was longer. On the third or fourth trial, a critical stimulus (e.g., a coloured spot) was presented unexpectedly in a quadrant of the cross within 2.3 degrees of fixation. On average, 25% of observers failed to detect the critical stimulus, thus providing evidence of inattentional blindness.
In subsequent research, Mack and Rock (1998) presented the critical stimulus at the fixation point and centred the cross about 2 degrees from fixation.
They expected that presenting the task in this way would eliminate inattentional blindness. In fact, however, detection rates for the critical stimulus dropped to between 40% and 60%! How did Mack and Rock interpret this finding? They argued that objects at fixation are typically the focus of attention.
However, when the task (i.e., comparing the arms of a cross) requires focusing attention away from fixation, attention to objects at fixation is actively inhibited.
There has been more research on change blindness than inattentional blindness. Why is change blindness an important phenomenon?
• Findings on change blindness are striking and counterintuitive and so require new theoret ical thinking.
• Research on change blindness has greatly clarified the role of attention in scene perception. That explains why change blindness is discussed at the end of the final chapter on perception and immediately before the chapter on attention.
• Experiments on change blindness have shed light on the processes underlying our conscious awareness of the visual world.
• Whereas most studies on perception consider visual processes applied to single stimuli, those on change blindness focus on dynamic processes over time.
Figure 4.11
Frame showing a woman in a gorilla suit in the middle of a game of passing the ball.
From Simons and Chabris (1999). Figure provided by Daniel Simons, www.theinvisiblegorilla.com.