This is known as the just noticeable difference JND, mentioned briefly in the above study comparing color perceptions of Chinese and Dutch participants or difference threshold. Unlike the absolute threshold, the difference threshold changes depending on the stimulus intensity.
As an example, imagine yourself in a very dark movie theater. If an audience member were to receive a text message on her cell phone which caused her screen to light up, chances are that many people would notice the change in illumination in the theater. However, if the same thing happened in a brightly lit arena during a basketball game, very few people would notice.
The cell phone brightness does not change, but its ability to be detected as a change in illumination varies dramatically between the two contexts. Webers Law : Each of the various senses has its own constant ratios determining difference thresholds. Webers ideas about difference thresholds influenced concepts of signal detection theory which state that our abilities to detect a stimulus depends on sensory factors like the intensity of the stimulus, or the presences of other stimuli being processed as well as our psychological state you are sleepy because you stayed up studying the previous night.
Human factors engineers who design control consoles for planes and cars use signal detection theory all the time in order to asses situations pilots or drivers may experience such as difficulty in seeing and interpreting controls on extremely bright days. While our sensory receptors are constantly collecting information from the environment, it is ultimately how we interpret that information that affects how we interact with the world. Perception refers to the way sensory information is organized, interpreted, and consciously experienced.
Perception involves both bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are built from sensory input, stimuli from the environment. On the other hand, how we interpret those sensations is influenced by our available knowledge, our experiences, and our thoughts related to the stimuli we are experiencing. This is called top-down processing. One way to think of this concept is that sensation is a physical process, whereas perception is psychological.
When we see our professor speaking in the front of the room, we sense the visual and auditory signals coming from them and we perceive that they are giving a lecture about our psychology class. Although our perceptions are built from sensations, not all sensations result in perception. This is known as sensory adaptation. Imagine entering a classroom with an old analog clock.
Upon first entering the room, you can hear the ticking of the clock; as you begin to engage in conversation with classmates or listen to your professor greet the class, you are no longer aware of the ticking. The clock is still ticking, and that information is still affecting sensory receptors of the auditory system. The fact that you no longer perceive the sound demonstrates sensory adaptation and shows that while closely associated, sensation and perception are different.
Additionally, when you walk into a dark movie theater after being outside on a bright day you will notice it is initially extremely difficult to see. If you are wondering why it takes so long to adapt to darkness, in order to change the sensitivity of rods and cones, they must first undergo a complex chemical change associated with protein molecules which does not happen immediately.
Now that you have adapted to the darkens of the theater, you have survived marathon watching the entire Lord of the Rings series, and you are emerging from the theater a seemly short ten hours after entering the theater, you may experience the process of light adaptation, barring it is still light outside.
During light adaptation, the pupils constrict to reduce the amount of light flooding onto the retina and sensitivity to light is reduced for both rods and cones which takes usually less than 10 minutes Ludel, So why is the process of raising sensitivity to light to adapt to darkness more complex than lowering sensitivity to adapt to light?
Caruso has suggested that a more gradual process is involved in darkness adaptation due to humans tendency over the course of evolution to slowly adjust to darkness as the sun sets over the horizon.
There is another factor that affects sensation and perception: attention. Attention plays a significant role in determining what is sensed versus what is perceived. Imagine you are at a party full of music, chatter, and laughter. You get involved in an interesting conversation with a friend, and you tune out all the background noise.
If someone interrupted you to ask what song had just finished playing, you would probably be unable to answer that question. 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. 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. 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.
It is not just vision that is affected by cultural factors. Sensation occurs when sensory receptors detect sensory stimuli.
Perception involves the organization, interpretation, and conscious experience of those sensations. Sensory adaptation, selective attention, and signal detection theory can help explain what is perceived and what is not.
In addition, our perceptions are affected by a number of factors, including beliefs, values, prejudices, culture, and life experiences. Not everything that is sensed is perceived. Do you think there could ever be a case where something could be perceived without being sensed? This would be a good time for students to think about claims of extrasensory perception. Another interesting topic would be the phantom limb phenomenon experienced by amputees. Please generate a novel example of how just noticeable difference can change as a function of stimulus intensity.
There are many potential examples. One example involves the detection of weight differences. What does it mean to sense something? Sensory receptors are specialized neurons that respond to specific types of stimuli. When sensory information is detected by a sensory receptor, sensation has occurred. For example, light that enters the eye causes chemical changes in cells that line the back of the eye. These cells relay messages, in the form of action potentials as you learned when studying biopsychology , to the central nervous system.
The conversion from sensory stimulus energy to action potential is known as transduction. You have probably known since elementary school that we have five senses: vision, hearing audition , smell olfaction , taste gustation , and touch somatosensation.
It turns out that this notion of five senses is oversimplified. We also have sensory systems that provide information about balance the vestibular sense , body position and movement proprioception and kinesthesia , pain nociception , and temperature thermoception.
Figure 1. The absolute threshold for detecting light is greater than you probably imagined—the human eye can see a candle on a clear night up to 30 miles away! The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold. Another way to think about this is by asking how dim can a light be or how soft can a sound be and still be detected half of the time. The sensitivity of our sensory receptors can be quite amazing. Under quiet conditions, the hair cells the receptor cells of the inner ear can detect the tick of a clock 20 feet away Galanter, It is also possible for us to get messages that are presented below the threshold for conscious awareness—these are called subliminal messages.
A stimulus reaches a physiological threshold when it is strong enough to excite sensory receptors and send nerve impulses to the brain: this is an absolute threshold. A message below that threshold is said to be subliminal: we receive it, but we are not consciously aware of it.
Therefore, the message is sensed, but for whatever reason, it has not been selected for processing in working or short-term memory. Over the years there has been a great deal of speculation about the use of subliminal messages in advertising, rock music, and self-help audio programs. Research evidence shows that in laboratory settings, people can process and respond to information outside of awareness. Figure 2. Priming can be used to improve intellectual test performance. Research subjects primed with the stereotype of a professor — a sort of intellectual role model — outperformed those primed with an anti-intellectual stereotype.
These days, most scientific research on unconscious processes is aimed at showing that people do not need consciousness for certain psychological processes or behaviors. One such example is attitude formation. The most basic process of attitude formation is through mere exposure Zajonc, Merely perceiving a stimulus repeatedly, such as a brand on a billboard one passes every day or a song that is played on the radio frequently, renders it more positive.
Interestingly, mere exposure does not require conscious awareness of the object of an attitude. In fact, mere-exposure effects occur even when novel stimuli are presented subliminally for extremely brief durations e.
Intriguingly, in such subliminal mere-exposure experiments, participants indicate a preference for, or a positive attitude towards, stimuli they do not consciously remember being exposed to. Another example of modern research on unconscious processes is research on priming. Priming generally relies on supraliminal stimuli, which means that the messaging may occur out of awareness, but it is still perceived, unlike subliminal messaging.
Supraliminal messages are be perceived by the conscious mind. For example, in one study, shoppers listened to either French or German music the supraliminal messaging while buying wine, and sales originating from either country were higher when music from that same country was played overhead. These lists contained words commonly associated with the elderly e. The remaining participants received a language task in which the critical words were replaced by words not related to the elderly.
After participants had finished they were told the experiment was over, but they were secretly monitored to see how long they took to walk to the nearest elevator.
The primed participants took significantly longer. That is, after being exposed to words typically associated with being old, they behaved in line with the stereotype of old people: being slow. Such priming effects have been shown in other domains as well. For example, Dijksterhuis and van Knippenberg demonstrated that priming can improve intellectual performance.
They asked their participants to answer 42 general knowledge questions taken from the game Trivial Pursuit.
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