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Sensation and Perception

Chapter 4
by

Gavin Williams

on 27 September 2016

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Transcript of Sensation and Perception

Perception
Sensation
Sensation: stimulation of sense organs
Sensation and Perception
Sight
Smell
Taste
Psychophysics
the study of how physical stimuli are translated into psychological experience
What you see elicits a reaction
Sensation begins with a detectable stimulus
Fechner: the concept of the threshold
Absolute threshold: detected 50% of the time
Just noticeable difference (JND): smallest difference detectable
Weber’s law: size of JND proportional to size of initial stimulus
Tendency to experience a stable perception in the face of continually changing sensory input
Signal-Detection Theory:
Sensory processes + decision processes=perception and behavior
Vision Stimulus
Light = electromagnetic radiation
Amplitude
Perception of brightness
Wavelength
Perception of Color
Purity
Saturation of color
Clear covering where light enters the eye
Opening that Regulates the amount of light.
Colored muscle
Constricts or dilates depending on amount of light
Lens
The lens focuses the light on to
the back of the Retina
Back of the eye that absorbs light and processes images
Figure 4.9 The retina
Figure 4.8 Nearsightedness and farsightedness
Optic disk: optic nerve connection/blind spotReceptor cells:Rods: black and white/low light visionCones: color and daylight vision
Figure 4.9 The retina
Adaptation to light
Figure 4.10 The process of dark adaptation
Becoming more or less sensitive to light as needed.
How vision affects the brain.
The main pathway is divided into two different visual channels
Parvocellular
Magnocellular
What?
Where?
Color
Brightness
Figure 4.15 The what and where pathways from the primary visual cortex
Hubel & Weisel
Feature detectors: Neurons that selectively respond to lines and edges.
Some feature detectors in the Temporal Lobe respond to faces
Short violet
Long Red
How do we see color?
Red, Blue, Green color receptors mix
Opponent processing theory
Trichromatic theory
Young and Helmholz
Hering
What about Yellow? For afterimages you need opposite colors that when on turn off their opposing color.
Red
/
Green
Blue
/
Yellow
Black/
White
Lateral antagonism
or lateral inhibition, occurs when neural activity in a cell opposes activity in surrounding cells.
Receptive Field
are the collection of rod and cone receptors that funnel signals to a particular visual cell in the retina
Hearing
The Ear
Sound
Much like light sound travels in waves
The vibration of the air molecules becomes sound
Amplitude
=Volume measured in decibels
Wavelength
=how high or low the sound is. the pitch
Timbre
=purity or complexity of sound
Wavelength is described in frequency which is measured in hz
Collects sound waves, the bigger the dish the better the signal.
The Pinna is part of the outer ear
Figure 4.46 The human ear
The Ossicles
Hammer, Anvil, Stirrup
These bones vibrate from the ear drum against the semicircular canal and cochlea to translate vibration into sound.
Inner ear- fluid filled coiled tunnel hair cells are lined up in the basilar membrane
Figure 4.47 The basilar membrane
1. Sound waves vibrate bones of the middle ear
2. Stirrup hits against the oval window of cochlea
Sets the fluid inside in motion
3. Hair cells are stimulated with the movement of the basilar membrane
4. Physical stimulation converted into neural impulses
5. Sent through the thalamus to the auditory cortex (temporal lobes)
The Auditory Pathway
How do we hear? What? I said...
Hermann von Helmholtz (1863) Place theory
Rutherford, 1886 Frequency theory
the frequency of the waves in the basilar membrane are interpreted as sound
Georg von Bekesy (1947)-Traveling wave theory
Ninja Lesson # 2
Ok your opponent has blinded you how do find them to throw your shuriken?
Two cues critical:
Intensity (loudness) can tell you how close your enemy is to you.
Timing of sounds arriving at each ear
Head as “shadow” or partial sound barrier
Timing differences as small as 1/100,000 of a second
allows you to find the sound.
Figure 4.48 Cues in auditory localization
Taste/Gustation
Soluble chemical substances stimulate receptor cells in taste buds
At the back of the tongue the bitter taste buds keep us from swallowing poisons, causing a gag reflex.
Food that has spoiled will often times be sour. Unhealthy sick people don't survive without medical attention
Sugar and sweet can is an indicator of energy necessary for survival.
Salt is necessary for our muscle function and neural function
Olfaction
Physical stimuli carried in the air stimulates the olfactory nerve
Does not go through the Thalamus
Memories are linked more strongly through the sense of smell
Touch
Physical stimuli = mechanical, thermal, and chemical energy impinging on the skin.
Touch
Temperature
Pain
Free nerve endings specific to cold or warmth
Free nerve endings that are divided in to fast and slow pain receptors.
Figure 4.53 Pathways for pain signals
Perception: selection, organization, and interpretation of sensory input
Perceiving Forms, Patterns, and Objects
Reversible figures
Perceptual sets
Inattentional blindness
Feature detection theory - bottom-up processing
Form perception - top-down processing
Subjective contours
Gestalt psychologists: the whole is more than the sum of its parts
Reversible figures and perceptual sets demonstrate that the same visual stimulus can result in very different perceptions
Perceiving Forms, Patterns, and Objects
Reversible figures
Perceptual Sets
Innattentional Blindness
Feature Detection Theory
Form Perception
Gestalt
a drawing that is compatible with two interpretations that can shift back and forth (see following slides for depiction
is a readiness to perceive a stimulus in a particular way.
involves the failure to see fully visible objects or events in a visual display.
people detect specific elements in stimuli and build them up into recognizable forms…bottom-up processing
Figure 4.22 Feature analysis in form perception
Top down processing, looking at the whole and moving down to the details.
Figure 4.23 Bottom-up versus top-down processing
Subjective Contours
The principle maintains that the human eye sees objects in their entirety before perceiving their individual parts
Figure-Ground
Proximity
Similarity
Continuity
Closure
a property of perception in which there is a tendency to see parts of a visual field as solid, well-defined objects standing out against a less distinct background.
How does that apply to your lives socially?
We lump like things together to make meaning out of them.
Simplicity
Distal vs. Proximal


To understand what perception does, you must understand the difference between the the proximal (~approximate = close) stimulus and the distal(~ distant) stimulus or object.
Your senses and your positioning vs. what you define what you are seeing as defined by you.
CONTEXT IS EVERYTHING
Depth and Distance perception
Binocular Cues
-cues from both of your eyes
Retinal Disparity
-objects within 25 feet project images to slightly different locations on the left and right retinas; thus each eye sees a slightly different view of the object)
Convergence
-convergence, feeling the eyes converge toward each other as they focus on a target.
Monocular Cues
-cues from a single eye
Motion Parallax
having images of objects at different distances moving across the retina at different rates.
It's why the moon stays in the sky and the building and the countryside fly by.
Accommodation
The feeling of the lens as it changes shape as the eye focuses.
Perceptual Constancies
Size
Pictoral Depth Cues
Linear Perspective
Parallel lines that run away from the viewer seem to get closer together.
Texture Gradient
As a Distance increases, a texture gradually becomes denser and less distinct.
Interposition
The shapes of near objects overlap or mask
those of more distant ones.
Relative Size
If separate objects are expected to be of the same size,
the larger ones are seen as closer.

When we know the size of the object we are able to adjust how it looks from what it should be
Height in Plane
Near objects are low in the visual filed; more distant ones are higher up.
Light and Shadow
Patterns of light and dark suggest shadows that can create an impression of three dimensional forms.
Visual Illusions
Muller-Lyer Illusion
Equal length lings look different because of outside cues.
Ponzo Illusion
Illusion works like Muler Lyer and converging lines convey perspectives.
Ames Box
Poggendorf Illusion
Upside-down T
Same length vertical and horizontal
Zollner Illusion
Impossible Figures
Fun Illusions
Look at the words below from left to right. Say out loud the COLOR not the word.
This is a left to right conflict. The right side of your brain tries to say the color while the left insists on reading the word.

This is the Bunny/Duck illusion. At first glance, what do you see? Now give it some time, but do not focus on one certain area, and then ask Yourself; what do I
really see? Now, look again. You might be surprised!!!!!!
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