Perception pdf

One of the most interesting demonstrations of how important attention is in determining our perception of the environment occurred in a famous study conducted by Daniel Simons and Christopher Chabris In this study, participants watched a video of people dressed in black and white passing basketballs.

Participants were asked to count the number of times the team in white passed the ball. During the video, a person dressed in a black gorilla costume walks among the two teams.

You would think that someone would notice the gorilla, right? Because participants were so focused on the number of times the white team was passing the ball, they completely tuned out other visual information.

Failure to notice something that is completely visible because of a lack of attention is called inattentional blindness. In a similar experiment, researchers tested inattentional blindness by asking participants to observe images moving across a computer screen. They were instructed to focus on either white or black objects, disregarding the other color. Read more on inattentional blindness at the Noba Project website. Motivation can also affect perception. Have you ever been expecting a really important phone call and, while taking a shower, you think you hear the phone ringing, only to discover that it is not?

If so, then you have experienced how motivation to detect a meaningful stimulus can shift our ability to discriminate between a true sensory stimulus and background noise. The ability to identify a stimulus when it is embedded in a distracting background is called signal detection theory. This might also explain why a mother is awakened by a quiet murmur from her baby but not by other sounds that occur while she is asleep.

Signal detection theory has practical applications, such as increasing air traffic controller accuracy. Controllers need to be able to detect planes among many signals blips that appear on the radar screen and follow those planes as they move through the sky. In fact, the original work of the researcher who developed signal detection theory was focused on improving the sensitivity of air traffic controllers to plane blips Swets, Our perceptions can also be affected by our beliefs, values, prejudices, expectations, and life experiences.

The shared experiences of people within a given cultural context can have pronounced effects on perception. For example, Marshall Segall, Donald Campbell, and Melville Herskovits published the results of a multinational study in which they demonstrated that individuals from Western cultures were more prone to experience certain types of visual illusions than individuals from non-Western cultures, and vice versa.

These perceptual differences were consistent with differences in the types of environmental features experienced on a regular basis by people in a given cultural context. In contrast, people from certain non-Western cultures with an uncarpentered view, such as the Zulu of South Africa, whose villages are made up of round huts arranged in circles, are less susceptible to this illusion Segall et al.

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In the Figure 3. So also the white background can be perceived as a vessel in the background of two faces. As said above, according to gestalt principle, the objects can be perceived meaningfully when they are grouped together. There are some principles which are followed by us in order to make our perception more meaningful.

Proximity means nearness. The objects which are nearer to each other can be perceived meaningfully by grouping them. The stars in the Figure 3. Stimuli need not be nearer to each other for perception. If there is similarity in these objects, they are grouped together and perceived, even if they are away. For example, in this Figure 3. Any stimulus which extends in the same direction or shape will be perceived as a whole Figure 3. For example, A in this figure though the curved line is broken, it is perceived as a continuous line, so also straight line is not seen with semicircles but as a continuous line B the dots are perceived as existing in the same line of direction continuously.

When a stimulus is presented with gaps, the human tendency is to perceive that figure as complete one by filling the gaps psychologically. For example, in the Figure 3. Objects which are having symmetrical shape are perceived as groups.

For example, the brackets of different shapes shown in the Figure 3. This refers to stableness in perception. We have a tendency to perceive the objects as relatively stable and unchanging in shape and size, inspite of a change in the image that we receive. Even then we perceive him as the same person. When we see people and houses from the top of hill, the images will be very small like Lillyputs. But we do not get confused by this. We perceive them correctly according to their actual size.

Perceptual constancy depends upon several factors like past experience, expectancy, habits, motivations, cognitive styles, learning, imagination, etc. There are different types of perceptual constancies. They are shape and size, brightness and colour, size constancy, etc. Ability of a person to perceive the distance is known as depth perception. This is very important ability to judge the distance between us and other people, objects and vehicles moving particularly when we are on roads.

This is also known as third dimension. The other two dimensions are left and right, and above and below. Depth perception is possible due to certain cues. These cues help us to understand the distance between one person and the other person or object. The distances separating the images of far objects appear to be smaller. For example, imagine that you are standing between railway tracks and looking off into the distance.

It appears that the tracks would seem to run closer and closer together at the other end. The nearer objects appear clearer than the distant objects. For example, a hill in far of distance appears farther away because the details do not seem clearly.

When one object obstructs our view of another, the front one appears nearer than the partly covered one. A gradient is a continuous change in something- a change without abrupt transitions.

Usually the regions closer to the observer have a coarse texture and many details. As the distance increases, the texture becomes finer and finer. This happens very gradually and gives a cue about the depth or distance.

In Figure 3. Sometimes the depth can be perceived when both eyes are used. This is called binocular cue.