Unit 4 - Sensation & Perception RG 4a - Intro. to S & P

Today’s Goals ● Can you: o Define sensation and perception o Discuss basic principles of sensory transduction, including absolute threshold, difference threshold, signal detection, and sensory adaptation. o Explain the role of top-down processing in producing vulnerability to illusion.

Sensation & Perception How do we construct our representations of the external world? To represent the world, we must detect physical energy (stimulus) from the environment and convert it into neural signals, a process called sensation. When we select, organize, and interpret our sensations, the process is called perception.

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain’s integration of sensory information. *We process this way when we have no prior knowledge. We start at the bottom and work our way up.

Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions drawing on our experience and expectations. Y-u c-n r-ad -hi- se-te-ce -it- ev-ry -hi-d l-tt-r m-ss-ng. The reason you can…is top-down processing! Your expectations and experiences let you fill in the blanks by making inferences on what you think “should” be there!

Top Down Processing: Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in what order the ltteers in a word are, the only iprmoetnt thing is that the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can still raed it wouthit a porbelm. This is bcuseae the human mind deos not raed ervey lteter by istlef, but the word as a wlohe.

Bottom-up and top-down processing work together to help us sort out complex images. Making Sense of Complexity “The Forest Has Eyes,” Bev Doolittle

Selective Attention *The focusing of conscious awareness on a particular stimulus. Ex.) Cocktail Party Effect: Your ability to attend to only one voice among many.

*Inattentional blindness- Failing to see visible objects when our attention is directed elsewhere. *Change blindness- (a form of inattentional blindness) Failing to notice changes in the environment. Ex.) Magicians

Thresholds Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. SensesThreshold Sight A candle flame at 30 miles on a clear, dark night Hearing The tick of a watch 20 feet way in a quiet room Smell One drop of perfume diffused throughout a three-room apartment Taste 1 teaspoon of sugar in 2 gallons of water Touch A bee’s wing falling on the cheek from 1 centimeter above

Signal Detection Theory (SDT) Predicts how and when we detect the presence of a faint stimulus (signal) amid background noise (other stimulation). Assumes that there is no single absolute threshold and detection depends on: ● Person’s experience ● Expectations ● Motivation ● Level of fatigue JOE!

Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND). *We need this to detect small differences among stimulus. *Students in the hallway must detect the sound of their friends’ voices amid all the other voices. *If you add 1 ounce to a 10-ounce weight, you will detect the difference; add 1 ounce to a 100-ounce weight and you probably will not.

Weber’s Law The size of the JND is proportional to the intensity of the stimulus ● if the stimulus intensity is high, the JND will be large (or it will take a bigger increase to notice the difference) ● if the stimulus intensity is low, the JND will be smaller (or it will take less of an increase to notice the difference)

Subliminal Threshold When stimuli are below one’s absolute threshold for conscious awareness. In other words…for most people these items are not consciously detected. HOWEVER…it is possible that some will notice these items!

Examples of “subliminal” messages in advertisements… In the spring/summer of 1990, Pepsi distributed a line of “Cool Cans” as part of a promotional campaign. All 4 of them are shown below… …the 2nd “NEON” can apparently had an “embedded” message if you stacked two cans together.. p

Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses…but will not impact a large group’s buying habits! Do the previous items really constitute subliminal messages? Do subliminal messages really influence our behaviors?

Subliminal Messages…Backmasking? It is recording technique in which a sound or message is recorded backward onto a track that is meant to be played forward. This is a deliberate process…currently the technique is being used to censor words or phrases for "clean" releases of songs. Backmasking was popularized by The Beatles, who used backward vocals and instrumentation on their 1966 album Revolver. Whether backmasked messages exist is a debate, as is whether backmasking can be used subliminally to affect listeners.

Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. Put a band aid on your arm and after a while you don’t sense it. After you initially get into a pool, it no longer feels cold. Let’s test the idea of sensory adaptation…

Sensory Adaptation – Marker Test Number your paper to 12… Each time I tell you to “SMELL”, please quickly sniff your marker and quickly rate the INTENSITY OF THE AROMA on a scale of 1 – 20 (1 = very slight smell 20 = very strong smell) What happened over the various trials? Quickly switch markers with your neighbor and rate the intensity of the aroma of their marker …