CH. 6: Sensation and Perception Flashcards
Sensation and perception are distinct
Sensation = input
Perception = interpretation of the input
Transduction
What takes place when sensors in the body convert physical signals from the environment into encoded neural signals sent to the central nervous system
Physical signals from environment –> encoded neural signals sent to the central nervous system
Translation of sensation to brain
- Occurs in rods and cones
Psychophysics (and signal detection theory)
Psychophysics: Methods that measure the strength of a stimulus and the observer’s sensitivity to that stimulus
- Developed by Gustav Fechner (1801–1887)
- Perceptions differ between people
- Absolute Threshold
- Just Noticeable Difference (JND)
Absolute threshold
Minimal intensity needed to just barely detect a stimulus (usually identification on 50% of trials)
Just noticeable difference (JND):
Minimal change in a stimulus that can just barely be detected
Sensory signals that are perceived among environmental “noise.”
Signal detection theory:
Response to a stimulus depends both on the person’s sensitivity to the stimulus in the presence of noise and on a person’s response criterion; takes into account individual perceptual sensitivity
- Used in military applications such as picking up a signal on a radar screen.
Multitasking
- Perception is active, and resources are limited.
- We use selective attention to focus in on chosen stimuli in our environment (and fail to perceive other stimuli)
- Multitasking involves paying attention to more than one stimulus at the same time.
- Experiments show that using a cell phone while driving increases the likelihood of an accident by four times.
- Hands-free phone operation is no exception.
- fMRI studies show decreases in brain areas during multitasking.
- People who frequently multitask often may have trouble focusing on one task.
Sensory adaptation
Sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions. This is a decreased response of the sensory receptors which reduce or stop sending impulses. Reduction in action potentials. Occurs in the brain.
- Adaptation is a useful process for most organisms.
- Our sensory systems respond more strongly to changes in stimulation than to constant stimulation.
- A changing stimulus warrants a response.
Habituation
A perceptual sensitivity decrease with repeated exposure
- This is a CNS response in the brain. The receptors are sending impulses but the CNS is tuning them out. No change in number of action potentials
Do we see reality as it is?
The brain as prediction source that fills the time gap involved in sensory processing
Visual Acuity: Ability to See Fine Detail
- Vision 20/20 refers to a measurement associated with a Snellen chart.
- It is the smallest line of letters that a typical person can read from a distance of 20 feet.
- Humans have receptors in their eyes that respond to wavelengths of light energy.
Light passing through the eyes
Light passes through the cornea, to the pupil, to the lens, and then to the retina.
Accommodation
Process by which the eye maintains a clear image on the retina
- If accommodation occurs improperly, myopia (nearsightedness) or hyperopia (farsightedness) may occur.
Retina
Light-sensitive tissue lining the back of the eyeball
Photoreceptor cells in the retina
Two types of photoreceptor cells in the retina contain light-sensitive pigments that transduce light into neural impulses.
- Cones and Rods
- Transduction occurs in rods and cones
Cones
Detect color, operate under normal daylight conditions, and allow us to focus on fine detail
Fovea
Area of the retina where vision is the clearest and there are no rods at all (only cones)
Rods
Become active under low-light conditions for night vision
ETC. ETC. about rods and cones and conversion of light to neural impulses
Slide 23
Perceiving Color
Color is our perception of wavelengths along the visible light spectrum.
- Cones are sensitive to red (long-wavelength), green (medium-wavelength), and blue (short-wavelength) light.
- All other colors are combinations (additive or subtractive color mixing) of these three wavelengths.
- Trichromatic color representation: The pattern of responding across the three types of cones that provides a unique code for each color
- Color deficiency/color blindness
Two color systems
Additive: red/green/blue (colored light ie. monitors)
Subtractive: red/yellow/blue (ie. paintings)
Single-Neuron Feature Detectors
Neurons that respond to specific orientations of edges. Here, a single neuron’s responses are recorded (left) as the monkey views bars at different orientations (right). This neuron fires continuously when the bar is pointing to the right at 45°, less often when it is vertical, and not at all when it is pointing to the left at 45°.
Troxler Effect
Sensory systems respond to change
Unchanging: we tend to not notice
Binding problem
How features are linked together by the brain so that we see unified objects in our visual world, rather than free-floating or miscombined features
Parallel processing
The brain’s capacity to perform multiple activities at the same time
Perceptual Grouping Rules
Principles first identified by Gestalt psychologists and now supported by experimental evidence demonstrate that the brain is predisposed to impose order on incoming sensations.
- See a unified whole rather than the parts
One neural strategy for perception involves responding to patterns among stimuli and grouping like patterns together.
Principles of Perceptual Organization
Gestalt principles characterize many aspects of human perception.
Gestalt grouping rules: How features and regions of things fit together, as in:
- Simplicity
- Closure
- Continuity
- Similarity
- Proximity
- Common fate - same direction
Hermann Illusion
Lateral inhibition: brain inhibits other neurons from responding
The Perceptual Constancies
Perceiving an object you are familiar with as having a constant shape, size and brightness despite the stimuli changes that may occur.
- Size Constancy
- Shape Constancy
- Color Constancy
- Lightness Constancy
- Distance Constancy
- Location Constancy
- Sound Constancy: Musical Instrument, Speech
Perceiving Distance and Size
Monocular depth cues: Aspects of a scene that yield information about depth when viewed with only one eye
- Relative size, familiar size, linear perspective, texture gradient, interposition, relative height
Binocular depth cues: Aspects of a scene in which depth cues are provided by two eyes working together.
Monocular cues
Relative Size - smaller further away
Interposition - front object closer
Aerial Perspective- hazy more distant
Linear Perspective- closer further away (railroad tracks)
Texture Gradient - less texture more distance
Motion Parallax - objects that are closer to us seen as moving faster than objects that are further away from us.
Familiar Size and Relative Size
When you view images of people, such as the people in the left-hand photo, or of things you know well, the object you perceive as smaller appears farther away.
Binocular Cues for depth/distance
Stereopsis - Retinal Disparity
- Line of sight for each eye straight ahead
Convergence - Muscle sense
- Line of sight converges to a single point
