Unit 4: sensation & perception Chapters 5 & 6

Sensation vs. Perception Sensation: a process by which our sensory receptors and nervous system receive and represent stimulus energy Sensation is the raw data our brain takes in from the environment.

Sensation vs. Perception Perception: a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events. Perception “makes sense” of sensation. Both involve one continuous process and perceptual failure may occur at any level whether at the sensory level or the perceptual interpretation level. Example: Prosopagnosia

Prosopagnosia – inability to recognize faces – face blindness https://www.youtube.com/watch?v=vwCrxomPbtY http://www.cbsnews.com/news/face-blindness-when- everyone-is-a-stranger-20-03-2012/

Bottom Up vs. Top Down Processing Bottom Up Processing: analysis that begins with the sense receptors and works up to the brain’s integration of sensory information. Involves making sense of raw sensation. Top Down Processing: Information processing guided by higher-level mental processes As when we construct perceptions drawing on our experience and expectations. Our expectations and experiences shape how we perceive information.

Making sense of the world Top-down processing: using models, ideas, and expectations to interpret sensory information What am I seeing? Bottom-up processing: taking sensory information and then assembling and integrating it Click to reveal definitions for bottom-up and top-down processing. Is that something I’ve seen before?

Bottom Up vs. Top Down

There are 13 Total!

Top-down Processing You may start to see something in this picture if we give your brain some concepts to apply: “tree” “sidewalk” “dog” “Dalmatian” Click to reveal sidebar and hints one by one.

Bottom Up Vs. Top Down What do you see?

Bottom Up vs. Top Down OLD WITCH IN PICTURE

Psychophysics study of the relationship between physical characteristics of stimuli and our psychological experience of them Light- brightness Sound- volume Pressure- weight Taste- sweetness

Sensation: Thresholds Absolute Threshold: minimum stimulation needed to detect a particular stimulus. Usually defined as the stimulus needed for detection 50% of the time.

Sensation: Thresholds Signal Detection Theory: predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) Assumes that there is no single absolute threshold What might a person’s detection of a stimulus depend on?

“Subliminal Messages” Stimuli you cannot detect 50% of the time Below one’s absolute threshold What does the research say? http://jeffmilner.com/backmasking/

PRESIDENTIAL ADS https://www.youtube.com/watch?v=L6pgoqZpfUU

Sensation: Thresholds Difference Threshold or (JND-Just Noticeable Difference): the minimum difference that a person can detect between two stimuli. What does it take to tell two similar stimuli apart? Weber’s Law: to perceive a difference between two stimuli, they must differ by a constant minimum percentage light intensity- 8% weight- 2% tone frequency- 0.3%

Weber’s Law (Ernst Weber) The JND is always large when the stimulus intensity is high, and small when the stimulus intensity is low 2 stimuli must differ by a constant proportion Example: Think volume of tv or radio (if the volume is low, then you only need to increase it a little to notice the difference, in contrast, if the volume is high, then you need to decrease it a significant amount to notice it) http://www.youtube.com/watch?v=zo7FpI8MmmE

Sensory Adaptation Sensory Adaptation: diminished sensitivity with constant stimulation. Ocean Bad Smell Ads- cut in, zoom, fade out

Automatic animation. Instructor: you can tell students, “This will push your motion sensors into sensory adaptation. For this to work, you must stare at the white dot in the center and never move your gaze. When the motion stops, quickly stare at a nearby doorway, window, or a face next to you. Decide now what you will look at.”

Sensory Adaptation and Vision

The Science of Energy and Sensation Transduction- conversion of one form of energy to another. Wavelength- the distance from the peak of one wave to the peak of the next. Hue- dimension of color determined by wavelength of light…color is matter of how far wavelengths are apart. Intensity- amount of energy in a wave determined by amplitude. brightness loudness

Vision: Physical Property of Waves Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Great amplitude (bright colors, loud sounds) Small amplitude (dull colors, soft sounds)

Human Vision Represents Narrow Part of All Electromagnetic Energy ROY G. BIV: Starts from longer to shorter wavelengths. R=longest; V=shortest

From Sensory Organs to the Brain The process of sensation can be seen as three steps: Reception-- the stimulation of sensory receptor cells by energy (sound, light, heat, etc) Transduction-- transforming this cell stimulation into neural impulses Transmission--delivering this neural information to the brain to be processed Automatic animation. Psychophysics refers to the study of the psychological effects of the forms of energy (heat, light, sound) that we can detect.

Sensations continued

Biology of Vision Step One: Light Enters the Eye 1.) Light enters the eye through the cornea: (transparent protector) and the light passes through the pupil: (small opening/hole). The size of the opening (pupil) is regulated by the iris: the colored portion of your eye that is a muscular tissue which widens or constricts the pupil causing either more or less light to get in.

Biology of Vision Step Two: An Image is Produced 2.) Behind the pupil, the lens, a transparent structure, changes its curvature in a process called accommodation, and focuses the light rays into an image on the light-sensitive back surface called the retina: where image is focuses.

The Eye Light from the candle passes through the cornea and the pupil, and gets focused and inverted by the lens. The light then lands on the retina, where it begins the process of transduction into neural impulses to be sent out through the optic nerve. The lens is not rigid; it can perform accommodation by changing shape to focus on near or far objects. Click to reveal bullets.

Visual Information Processing The images we “see” are not made of light; they are made of neural signals which can be produced even by pressure on the eyeball. Once neural signals enter the optic nerve, they are sent through the thalamus to the visual cortex. No animation. Instructor: the first bullet point can be demonstrated by the activity suggested on page 230 of the text (closing eyes, turning eyes to the left, pressing on the right corner of they eyelid). It can also be demonstrated by mentioning, “Maybe this is why people are said to “see stars” when they get punched hard in the head.”

Biology of Vision Step Three: Chemical Reactions and Sight 3.) Image coming through activates photoreceptors in the retina called rods and cones. As rods and cones set off chemical reactions they form a synapse with bipolar cells which forms a synapse with ganglion cells which fire action potentials along the optic nerve: that carries this information to be processed by the Thalamus: (sensory switchboard) that sends information to the visual cortex which resides in the occipital lobe. The brain then constructs what you are seeing and turns image right side up.

Photoreceptors: Rods and Cones When light reaches the back of the retina, it triggers chemical changes in the receptor cells, called rods and cones. The rods and cones in turn send messages to ganglion and bipolar cells and on to the optic nerve. Rods help us see the black and white actions in our peripheral view and in the dark. Rods are about 20 times more common than cones, which help us see sharp colorful details in bright light. Click to reveal bullets and example. Instructor: have students see if they can guess which objects in the picture are cones and which are rods; the shape implied by the names should be a big hint.

Parts of Retina fine detail and color vision Blind Spot: part of retina where optic nerve leaves the eye…no receptor cells are there. Brain fills information in with info from other eye. Fovea: central focal point of the retina, where cones cluster. Cones: located near center of retina (fovea) fine detail and color vision daylight or well-lit conditions Rods: located near peripheral retina detect black, white and gray twilight or low light

Errors In Vision Acuity: the sharpness of vision Nearsightedness: nearby objects seen more clearly lens focuses image of distant objects in front of retina Farsightedness: faraway objects seen more clearly lens focuses near objects behind retina

Errors in Vision

Visual Involves Parallel Processing Parallel vs. Serial: parallel means simultaneous while serial means step by step. Our brains process are often parallel processes while computers work serially. Parallel Processing: simultaneous processing of several dimensions through multiple pathways. Different part of brain for: color motion form depth

Parallel Processing Turning light into the mental act of seeing: light waveschemical reactionsneural impulsesfeaturesobjects and one more step... Parallel processing refers to building perceptions out of sensory details processed in different areas of the brain. For example: Click to reveal bullets and example.

Parallel Processing Feature Detectors: neurons in the visual cortex respond to specific features shape angle movement

How The Brain Perceives

Visual Information Processing Trichromatic (three color) Theory Young and Helmholtz three different retinal color receptors red green blue

Color Vision We see the color of an orange because it absorbs all light except the wavelengths that our brain interprets as orange. You could note that the red, green and blue don’t actually refer to the appearance of the cones; they are the colors to which these three cones react. No animation. Instructor: you could start by saying that we see the color of an orange because it absorbs all light except the wavelengths that our brain interprets as orange. You could note that the red, green and blue don’t actually refer to the appearance of the cones; they are the colors to which these three cones react.

Color Deficient Syndrome People who suffer red-green blindness have trouble perceiving the number within the design

Visual Information Processing Opponent-Process Theory- opposing retinal processes enable color vision. Example: Jesus On Title Slide. “ON” “OFF” red green green red blue yellow yellow blue black white white black

Opponent-Process Theory Test Instructor: Tell the students: “Stare at the center dot for 30 seconds; if you’re doing it well, the flag will start to disappear. If it does, keep staring at the dot.” Further narration as they stare at the dot: “If opponent-process theory is correct, then fatiguing our perception of one will make a blank slide look like the opposite color… and the opponent processes are white vs. black, red vs. green, and yellow vs. blue.” Click to make flag disappear. What do you see? Question for students: “Besides opponent-process theory, what else are we demonstrating here?”...(sensory adaptation). After our color receptors for green become fatigued, an empty white background will briefly seem red, just as plain water might taste salty or strange after eating a lot of intensely sweet candy to the point of fatiguing our tongue. There have been versions of this circulating online in which our receptors get fatigued just by some dots near the center dot, and a B&W picture turns to full color when we look at a blank space. The dot, the dot, keep staring at the dot in the center…

Mariachi or Old Folks

3 Faces In One

9 People?

Old Man or Lovers Kissing

A Young Woman or…

A Grouchy Clown

A Clown…

Or a Circus

Color Constancy Human Beings maintain Color Constancy: perceiving familiar objects as having consistent color, even if lighting changes to alter the wavelength given off by the object.

http://www.brainbashers.com/showillusion.asp?129

Context Affects Color We only retain color constancy when the context remains the same. Same color will look different when compared in different contexts.