Attention and Inattention
People are constantly bombarded with stimuli—sights, sounds, odors, feelings, and so on. To avoid being overwhelmed, people engage in selective attention by choosing certain stimuli in the environment to process while ignoring the rest. Yet the filtered information may still influence how attended-to information is interpreted. This is easily demonstrated by divided attention tasks, which require individuals to attend to multiple sources of information at once. One such task is called dichotic listening. In this task, a listener wearing headphones receives one message in the right ear and another in the left. The listener is asked to attend to only one message and repeat it word for word, called shadowing. The messages stop after a period of time, and the listener is quizzed on the material played to the nonshadowed ear. The listener's interpretation can be influenced by what is played in each ear. If the sentence "They were throwing rocks at the bank" is played in the shadowed ear, the word bank is more likely to be interpreted as a financial institution if the word money is simultaneously played in the nonshadowed ear. If the word stream is played in the nonshadowed ear, the bank is more likely to be interpreted as the side of a river. Individuals can typically remember only superficial aspects of the nonshadowed message, such as whether the speaker was male or female, the number of people speaking, and a little about the topic of the message. Regardless of whether they are consciously aware of the information played to the nonshadowed ear, some aspects of the message still come through.
A similar example is the cocktail party effect. People are often unaware of conversations taking place outside of their particular group at a party. However, if someone in another group casually mentions their name, they immediately become aware of it. The cocktail party effect is a form of selective attention. Individuals attend easily to their own name, as it is a familiar stimulus. Therefore, they will filter out other stimuli upon hearing their name.
Inattentional Blindness and Change Blindness
Inattentional blindness is the failure to notice an unexpected object or event when one's attention is focused on something else. For example, in 1983, psychologists Robert Becklen and Daniel Cervone conducted a study in which people were told to count the number of times men wearing white shirts in a video passed a basketball. In the middle of the video, a woman carrying a large white umbrella was superimposed on the film. She appeared to walk right through the group of men. Only 20 percent of the viewers noticed the woman. Inattentional blindness has been replicated using other stimuli that viewers failed to notice. In traffic accidents involving a pedestrian, bicyclist, or motorcyclist, car drivers will often report they never saw the person they hit. Their attention was focused on looking for oncoming cars, and they simply did not see anything else.
Change blindness is the failure to notice a change in a stimulus event. In 1998, cognitive psychologists Daniel Simons and Daniel Levin conducted a study in which an experimenter held a map and asked a random pedestrian for directions. As the pedestrian and experimenter were looking down at the map, two people walked in between them holding a large wooden door that blocked their view of each other. During this interruption, the experimenter switched places with one of the door carriers. This second person looked and sounded nothing like the experimenter. However, nearly half the pedestrians failed to notice they were talking to a different person.