两耳分听
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Overview
资料来源： 实验室的乔纳森 Flombaum — — 约翰 · 霍普金斯大学
它是众所周知的事实，处理传入刺激人类能力很有限。然而，世界是复杂的并总是有很多事情一次。选择性注意是允许人类和其他动物来控制哪些刺激得到处理而成为被忽略的机制。想想一个鸡尾酒会： 一个人可能不能参加所有的谈话，一次发生。然而，每个人都有能力来有选择地听一个对话，领先所有剩下的成为对无人值守和什么比背景噪声。为了研究人怎么这样，研究人员通过播放声音向与会者 dichotically，即给每只耳朵同时播放不同的声音模拟鸡尾酒会环境更容易控制。这就被所谓的双耳分听范式。
本实验演示与叫做两耳分听研究选择性听觉注意的标准程序。
Procedure
Results
The graph in Figure 1 shows the percent of questions answered correctly by condition. The red dotted line (at 20%) shows expected guessing performance (chance), given that each question included five choices. The participant was able to answer more questions correctly for the attended compared to the unattended passage, reflecting the ability to attend selectively to a single stimulus when more than one is present. But the participant also answered more questions correctly in the one passage baseline condition compared to the attended condition. This demonstrates the difficulty of attending selectively, and the limited capacity of human attention.
Figure 1. Results from dichotic listening experiment. Shown are the percent of questions answered correctly by condition.
Applications and Summary
Dichotic listening has been used for many purposes to understand the nature and capacities of selective attention. For example, it has been used with a concurrent visual task to investigate the extent to which visual and auditory attention compete with one another—an important issue for understanding when and how humans are able to multitask.
One of the most influential applications of the paradigm has been in the study of the human brain’s lateralization for processing language. The human brain is divided into two hemispheres. Generally speaking, the right hemisphere is wired to the left side of the body, and the left hemisphere is wired to the right. This means that auditory stimuli played exclusively to one ear will be routed, first, to the opposite brain hemisphere. It is also known that the left hemisphere is generally specialized for language processing. Therefore, the prediction is that stimuli played to the right ear should be processed more effectively than stimuli played to the left ear. This has been confirmed in many dichotic listening studies, and it makes dichotic listening a useful paradigm for investigating language deficits thought to be associated with left hemisphere brain damage, as often occurs after a stroke, but without using a brain scan.
Transcript
Dichotic listening is a paradigm used to characterize the nature and capacities of selective attention.
Selective attention is the mechanism that allows humans and other animals to control which stimuli are processed and which are ignored.
For instance, think of a cocktail party where there are many conversations taking place at once. An individual can focus their attention to listen to only one conversation, which will lead the rest to become nothing more than background noise.
This video demonstrates a dichotic listening paradigm, which involves playing different auditory stimuli simultaneously to each ear. You will learn how to design and perform, as well as how to analyze and interpret an experiment investigating selective auditory attention.
During this experiment, participants complete two listening sessions: the first measures baseline listening comprehension, and the second involves dichotic listening. Participants are asked to pay attention and listen carefully.
For the baseline session, a single passage is played through the headphone attached to the right ear. Nothing is played in the left ear.
During the dichotic listening session, one passage is played through the right ear, and a different passage is played simultaneously in the left ear. Participants are asked to only attend to the passage played in their right ear.
After each session, participants are given a set of comprehension questions that are associated with the recorded passages. In this case, the dependent variable is the number of comprehension questions answered correctly after each passage.
Participants are expected to answer more answers correctly for the attended passage compared to the unattended passage.
To create the stimuli for the experiment, select three different passages with information content that can be tested for comprehension. Record one person reading the selected pieces. Make sure to save each recording into individual audio files.
In relation to the passages, you will need two sets of headphones connected to the audio source to easily play separate auditory clips, and printed copies of the comprehension questions for the participant to complete after the listening sessions.
To begin the study, inform the participant that they will put on headphones to hear a short passage delivered to their right ear. Instruct the participant to pay attention and listen carefully, as they must answer questions about the passage afterwards.
After the participant puts on the headphones, play one of the passages through the side attached to the right ear. Note that nothing is played through the left ear.
Once the passage has finished playing, have the subject remove the headphones and give them a set of associated questions. Allow them 15 min to answer as many as possible.
To initiate the dichotic session, inform the participant that they will put on the headphones again, but will hear two different passages played simultaneously in each ear.
This time, instruct the participant to pay close attention to the passage in one ear and ignore the reading in their other ear. Press play at the same time to start the two different passages in each ear.
When the recordings are over, ask the participant to answer questions from both passages—the attended and unattended—within 30 min.
After the participant has finished answering the questions, score the answers as being correct or incorrect.
To analyze the data, calculate the proportion of correct answers associated with each individual passage. Graph the average percent correct by passage.
When selective attention was required, participants’ performances declined, but they answered more questions correctly for the attended compared to the unattended passage. These findings demonstrate the difficulty of selectively attending to stimuli—that a limited capacity of attention exists.
Now that you are familiar with how dichotic listening is used to study selective attention, let’s take a look at how this method is applied in other research studies.
The dichotic listening task is a very useful paradigm for evaluating language deficits associated with brain damage, such as after a stroke.
Generally speaking, the right hemisphere is wired to the left side of the body, and the left hemisphere is wired to the right. Such connections mean that auditory stimuli played exclusively to one ear will first be routed to the opposite brain hemisphere.
Given that the left hemisphere is specialized for language processing, auditory stimuli played to the right ear should be processed more effectively than stimuli played to the left ear. Thus, this paradigm can assess brain damage without the use of a brain scan.
Dichotic listening can also be combined with simultaneous tactile stimuli to study how the brain integrates multisensory information—an important issue for understanding when and how humans are able to multitask.
You’ve just watched JoVE’s introduction to investigating selective attention through a dichotic listening paradigm. Now you should have a good understanding of how to design and conduct this type of study, and how to analyze and interpret the results.
Thanks for watching!