Sensation & Perception How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we give meaning by selecting, organizing, and interpreting our sensations, the process is called perception. OBJECTIVE 1| Contrast sensation and perception, and explain the difference between bottom-up and top-down processing.

Sensation vs. Perception The experience of sensory stimulation Perception The process of creating meaningful patterns from raw sensory information

Law of Closure!

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

THE CHT Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. Type of perceptual set/expectancy-tendency to perceive things in a certain way because their previous experiences influence them THE CHT

Top Down Processing Backmasking Freeze, then video

You try it! Whisper the words on the next slide to yourself. Ready, set, go…..

Example of Top-Down Processing Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

Bottom-up processing: see color, angles, lines that create image of horse, rider, etc. Top-down processing: consider title, notice expressions, make conclusion about painting

Another Example Charlie Chaplin video Dragon Face Illusion

Selective Attention Focusing of conscious awareness on a particular stimulus Stop! Think about your socks! Do you suddenly feel the soft fabric pressing against your feet? Were you feeling your socks before?

Problems with Selective Attention Receiving a phone call while driving

You try it! I am going to show you a media clip to test your attention. Please count the number of times that the players in white shirts throw the basketball. Make sure to stay silent for the duration of the clip, so everyone can pay attention. Let’s play ball!

Inattentional Blindness Failing to see visible objects when our attention is directed elsewhere Daniel Simons and Christopher Chabris Half of their participants failed to see the gorilla Let’s try that again.

Change Blindness Failing to notice changes in the environment Happened in 2/3 of Simon’s participants Door Study

More Examples! Do the Test videos https://www.youtube.com/watch?v=ubNF9QNEQLA https://www.youtube.com/watch?v=Ahg6qcgoay4

Transduction Converting one form of energy into another, such as transforming stimuli such as sight into neural impulses our brain can interpret

Thresholds Absolute threshold Signal detection theory Subliminal stimulation Difference threshold Psychophysics-the study of the relationship between the physical characteristics of our stimuli, such as their intensity, and our psychological experience of them

Sensory Thresholds Developed by Gustav Fechner Absolute threshold The minimum amount of energy that can be detected 50% of the time Developed by Gustav Fechner

Detection Absolute Threshold Intensity No No No Yes Yes Detected Observer’s Response Detected Tell when you (the observer) detect the light.

Signal Detection Theory (SDT) Predicts how and when we detect the presence of a faint stimulus (signal) amid background noise (other stimulation). SDT assumes that there is no single absolute threshold and detection depends on: Person’s experience Expectations Motivation Level of fatigue Ex. Mother waking up to her child’s faintest whimper Carol Lee/ Tony Stone Images

Signal Detection

Subliminal Stimulation Stimuli we detect less than 50% of the time are subliminal stimuli Examples Cloth fibers floating onto one’s skin Faint whispers

Subliminal Stimulus-Priming Unconscious activation of certain associations In an experiment, participants were briefly flashed a positive scene (a loving couple) followed by an image of a person. Separately, participants were briefly flashed a negative scene (dead body) followed by an image of a person. Participants had a more positive opinion of the first image than the second. F-O-L-K S-O-A-K What do we call the white of an egg?

Sensory Thresholds Difference threshold The smallest change in stimulation that can be detected 50% of the time Also called the just noticeable difference (jnd) Raising the volume on the tv

Difference Threshold Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND). Difference Threshold No No Yes Observer’s Response Tell when you (observer) detect a difference in the light.

What if??? You add one pound of gold to a ten pound pile of gold. Will you notice a different in the weight of the gold? You add one pound of gold to one hundred pounds of gold. Will you notice a difference in the weight of gold? Quarter experiment So….

Ernest Weber Weber realized that it is not the amount that makes the difference threshold but a proportion. He developed Weber’s law. So adding 1% more gold to each pile will make a difference.

Weber’s Law Stimulus Constant (k) Light 8% Weight 2% Tone 3% Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Stimulus Constant (k) Light 8% Weight 2% Tone 3%

Sensory Thresholds Weber’s Law States that the difference threshold is a constant proportion of the specific stimulus Senses vary in their sensitivity to changes in stimulation Envelop and coin demonstration. More than just sensation, it has to do with sales.

Sensory Adaptation An adjustment of the senses to the level of stimulation they are receiving Ever forgotten you are wearing a watch? Ever gotten used to a smell, such as garbage? Do you still smell the fragrance when you walked in my room??? Does the pool water get warmer after you have jumped into a pool? Then why don’t things disappear from your vision? (our eyes are always moving)