Chapters 5 & 6 - Loudoun County Public Schools

Chapters 5 & 6 - Loudoun County Public Schools

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:


Bottom Up Processing: analysis that begins with the sense receptors and works up to the brains 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 What am I

seeing? Bottom-up processing: taking sensory information and then assembling and integrating it Top-down

processing: using models, ideas, and expectations to interpret sensory information Is that something Ive 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


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 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 persons detection of a stimulus depend on? SUBLIMINAL MESSAGES Stimuli you cannot detect 50% of the time Below ones absolute threshold

What does the research say? PRESIDENTIAL ADS 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? Webers 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% WEBERS 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) SENSORY ADAPTATION Sensory Adaptation: diminished sensitivity with constant stimulation.


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 lightcolor is matter of how far wavelengths are apart. Intensity- amount of energy in a wave determined by amplitude. brightness loudness NARROW PART OF ALL ELECTROMAGNETIC ENERGY ROY G. BIV:

Starts from longer to shorter wavelengths. R=longest; V=shortest VISION: PHYSICAL PROPERTY OF WAVES Short wavelength=high frequency (bluish colors, high-pitched sounds)

Great amplitude (bright colors, loud sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Small amplitude (dull colors, soft sounds)

SENSATIONS CONTINUED 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) Transductio n-transforming this cell stimulation into neural

impulses Transmissio n--delivering this neural information to the brain to be processed 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 lightsensitive 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. 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. 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. PARTS OF RETINA

Blind Spot: part of retina where optic nerve leaves the eyeno 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


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 waveschemical reactionsneural impulsesfeaturesobjects and one more step...

Parallel processing refers to building perceptions out of sensory details processed in different areas of the brain. For 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 We see the colorVISION 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 dont actually refer to the appearance of the cones; they are the colors to which these three cones react. COLOR DEFICIENT SYNDROME People who suffer redgreen

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 The dot, the dot, keep staring at the dot in the center



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. CONTEXT AFFECTS COLOR We only retain color constancy when the context remains the

same. Same color will look different when compared in different contexts.

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