Unit 4: Sensation & Perception Module 12 & 13

Sensation & Perception Sensation: the process by which you detect physical energy from your environment and encode it as neural signals. In other words, how we receive information from our environment. 5 Senses: See, hear, touch, taste, & smell.

Sensation & Perception Perception: the process that organizes sensory information and makes it meaningful. This is what our body does with the information we sense. It processes the information and transforms it into something we recognize.

Figure 4.23 Bottom-up versus top-down processing

Sensation & Perception Psychophysics: the study of how physical stimuli (light, sound…) are translated into psychological experience. Can you detect a stimulus, identify it, differentiate between it and another stimulus, and describe the magnitude of this difference?

Thresholds Stimulus: a change in environment that can be detected by sensory receptors. (Light, sounds, flavors, …) Absolute threshold: the weakest level of a stimulus that can be correctly detected at least half the time (50%). Your absolute threshold is when you could detect a sound, light, etc. half the time.

Thresholds The 50-50 recognition point defines your absolute threshold.

Thresholds Signal detection theory: minimum threshold changes with fatigue, attention, expectations, motivation, emotional distress, and from one person to another. Ex. I can spot gum chewing even when you try to hide it! I can hear the chew and see subtle movements in your mouths!

Thresholds Subliminal stimulation: receiving messages below one’s absolute threshold for conscious awareness. They can have a momentary, subtle effect on thinking. (Subliminal messages) Information processing occurs automatically unbeknownst to our conscious mind.

Thresholds Difference threshold: minimum difference between any two stimuli that a person can detect 50% of the time. Just noticeable difference (JND): when you experience the difference threshold. Ex. Adding one penny to a container with 10 pennies is more noticeable than if it had 100 pennies in it.

Two objects must differ by 2% to notice. Thresholds Weber’s Law: two stimuli must differ by a constant minimum percent (rather than a constant amount). Two objects must differ by 2% to notice.

Thresholds Sensory adaptation: diminished sensitivity because of constant stimulation. Put a band aid on your arm and after a while you don’t feel it.

Selective Attention Selective attention: the focusing of conscious awareness on a particular stimulus. Focusing on one thing allows us to block out other things going on. Did you notice that your nose is in your line of vision?

Selective Attention Cocktail party effect: ability to focus on one voice in a room full of people speaking. Inattentional blindness: failing to see visible objects when our attention is directed elsewhere. Change blindness (changing person) Change deafness (changing speaker) Choice blindness (changing choice)

Selective Attention Pop-out Phenomenon: When a stimulus draws your eye, you can’t help but notice. It demands your attention.

Module #13: Vision

Vision Transduction: transformation of stimulus energy (light, sound, smells, etc.) to neural impulses our brains can interpret. Our senses receive the information and then, through transduction, our brains interpret them.

Spectrum of Electromagnetic Energy The rest of these sources of energy are invisible to us. Visible Spectrum

VISION Wavelength: the distance from one wave peak to the next. It determines the hue. Amplitude: height of the wave.

VISION Hue: the color we see. 400 nm 700 nm Long wavelengths Violet Indigo Blue Green Yellow Orange Red 400 nm 700 nm Short wavelengths Long wavelengths

Different intensities of blue. VISION Intensity: (brightness) Amount of energy in a wave determined by the amplitude. Different intensities of blue.

The Eye

The Eye Cornea: where light enters the eye. Pupil: regulates the amount of light. Iris: colored ring of muscle, constricts or dilates depending on the amount of light. Lens: focuses the light rays on the retina. Acuity: The sharpness of vision.

The Retina Retina: absorbs light, processes images. Contains rods and cones. The image formed on your retina is upside down and incomplete. Your brain fills in information and straightens out the upside down image almost immediately.

The Retina Rods: detects black & white & allows you to see in low light. Used for night vision. Cones: detects color & allows you to see in bright light. Most concentrated at the fovea.

The Eye Normal Vision: Rays of light converge on the retina for both nearby and distant images.

The Eye Nearsighted: nearby objects are seen more clearly than distant objects. I could see near! The light rays from distant objects focus in front of the retina. When it actually reaches the retina, the image is blurry.

The Eye Farsighted: distant objects are seen more clearly than nearby objects. I could see far! The light rays from nearby objects focus behind the retina resulting in a blurry image.

Correcting Our Vision We can correct our vision by adjusting the lens in our eyes to focus images directly on the retina. LASIK – laser eye surgery in which a flap is cut into the cornea to access tissue behind it. PRK – laser to reshape the surface of the cornea.

Optic Nerve, Blind Spot, & Fovea Optic nerve: Carries neural impulses from the eye to the brain. Fovea: Central point in the retina where cones (no rods) cluster. Point where images focus. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. Let’s find your blind spot!!!!

Optic Nerve, Blind Spot, & Fovea

Visual Pathway Feature detectors: individual neurons in the primary visual cortex/occipital lobes that respond to specific features of a visual stimulus. Neurons only respond to vertical, horizontal, or diagonal lines. They detect edges, angles, and movement.

Visual Pathway Parallel Processing: simultaneously analyzing different elements of sensory information, such as color, brightness, shape, etc. Different parts of the brain are responsible for different functions.

 Color Vision Young-Helmholtz Trichromatic theory: retina has 3 types of color receptors for red, blue, and green. Stimulating a combination of these 3 colors results in other colors. Ex. Stimulating red and green cones produces a yellow image. People who are color blind have color cones that aren’t functioning.

 Color Vision Opponent-Process Theory: opposing retinal processes enable color vision. Red & Green, Yellow & Blue, White & Black. Afterimages: images continue to briefly appear even after the actual image is removed. Staring at a color will tire that color’s cones and its opponent color appears.

Color Constancy Color depends on context. The three blue disks are identical in color!