Subliminal Perception
Humans are constantly perceiving visual and auditory stimuli. Sometimes our perception of these stimuli occurs consciously ,we are aware of a stimulus and know that we are perceiving it. But our perception of a stimulus can also occur without our awareness: an image might appear and disappear before our eyes too quickly for us to notice that we saw it, or a sound might be too faint for us to realize that we heard it. This phenomenon – the perception of a stimulus just below the threshold of conscious awareness – is called subliminal perception. Experiments have shown that subliminally perceived stimuli can influence people’s thoughts and attitudes.
听力材料：
Now, listen to part of a lecture on this topic in a psychology class.
(male professor) Consider this experiment. Two groups of people were asked to watch TV and while they are watching a picture flashed on the screen less than a second, very quickly so it was barely noticeable.The picture was a boy with a birthday cake. Now, like I said, there were two groups and each group saw a slightly different version of the picture. One group got the boy looking angry, in fact, he was actually throwing the cake on the floor. The other group got a picture of the boy smiling, happy, holding up the cake like he was offering it. Same boy, same cake but different emotions expressed in each picture.Everyone was then asked to look at a different image. Now, this is a third image, right? Again, it's the boy and the cake, but this time the image stayed on the screen. In this picture, the boy's just holding the cake basically no emotion on his face, everything very neutral.Now, remember, nobody knew they’d already seen a picture of this boy. After a minute, everyone was asked to describe the boy’s personality. Those who’d been exposed to the image of the angry boy, they generally described the boy’s personality negatively. Those who’d earlier seen the happy boy described him, well, positively."
Question：
Describe what subliminal perception is and explain how the experiment discussed by the professor illustrates this phenomenon.
