Sensation and Perception Flashcards
Distinction Between Physical and Perceptual
Physical: Actual external stimuli.
Perceptual: Individual interpretation of stimuli.
Example: Misidentifying sounds or images due to expectation or context.
Seven Steps of the Perceptual Process:
Seven steps, plus “knowledge” inside the person’s brain, describe the process of perception.
These steps occur between the time a person looks at the stimulus in the environment (e.g., a tree), perceives the stimulus, recognizes it, and takes action toward it
Distal Stimulus
Proximal Stimulus
Receptor Processes
Neural Processing
Perception
Recognition
Action
Distal Stimulus
Object in the environment. Observer selectively attends to objects.
Proximal Stimulus
The representation of the distal stimulus on the receptors.
Stimulus is “in proximity” to the receptors Image on sensory receptors.
Receptor Processes
Sensory receptors are cells specialized to respond to environmental energy.
Visual pigment is what reacts to light.
Transduction occurs, which changes environmental energy to nerve impulses.
The end result is an electrical representation of the tree.
Neural Processing
Signals are transmitted and processed in the brain.
Neural processing - changes that occur as signals are transmitted through the maze of neurons
Primary receiving area
Occipital lobe
Temporal lobe
Parietal lobe
Perception
Awareness of stimulus.
Recognition
Categorization of stimulus.
Action
Response to stimulus.
Top-Down vs. Bottom-Up Processing
Bottom-Up (Data-Driven): Processing based on incoming stimuli from the environment
Top-Down (Knowledge-Based): Influenced by prior knowledge and expectations.
Absolute Threshold
the smallest amount of energy needed to detect a stimulus
Difference Threshold
The smallest detectable difference between two stimuli that a person can define
Principles of Transformation and Transduction
Transformation: When the stimuli and responses created by stimuli are transformed, or changed, between the environmental stimuli and perception.
Transduction converts environmental energy into electrical signals.
Magnitude Estimation
How perceived stimulus intensity does not always match actual intensity.
Perceptual World
Relationship between stimuli and perception above the threshold.
Method of Limits
Vary level of stimulus from low to high or reverse and note at what point the subject changes from detecting something to not, then switch directions. Average over many trials to determine threshold.
Method of Adjustment
Continuous adjustment of stimulus intensity.
Method of Constant Stimuli
Randomized stimulus levels to determine 50% detection rate.
Step 1and 2 of the Perceptual Process Explanation
Step1: Information about the tree (the distal stimulus) is carried by light.
Step 2: The light is transformed when it is reflected from the tree, when it travels through the atmosphere, and when it is focused on by the eye’s optical system. The result is the proximal stimulus, the image of the tree on the retina, which is a representation of the tree.
Specificity Coding
A specialized neuron that responds only to one concept or stimulus (e.g., “the grandmother cell”)
Sparse Coding
Small groups of neurons respond to stimuli.
Occurs when a particular stimulus is represented by a pattern of firing of only a small group of neurons.
Population Coding:
Large patterns of neuron activity represent stimuli.
Proposes that our experiences are represented by the pattern of firing across a large number of neurons.
Electrical Signals in Neurons
Action potentials are brief electrical signals lasting ~1 millisecond.
Remain constant in size, with increased stimulus intensity causing higher firing rates.
Synaptic Transmission
Neurotransmitters bridge the gap between neurons, fitting specific receptor sites.
Mind–Body Problem
The challenge of explaining how physical neural processes relate to subjective perception.
Brain Imaging
Differentiates structural (anatomical) and functional (activity-based) connectivity in the brain.
Highlights modularity (specific brain regions for specific functions) and distributed representation (multiple areas involved in processing).
Light and Vision
Visible light ranges from 400–700 nanometers.
The retina processes reflected light using rods and cones.
Focusing Mechanisms
The cornea handles 80% of focusing, while the lens (adjustable) accounts for 20%.
Presbyopia (aging lens): Difficulty focusing on nearby objects. Due to hardening of lens and weakening of ciliary muscles.
Myopia (nearsightedness): inability to see distant objects clearly. Image is focused in front of retina.
Hyperopia (farsightedness): inability to see nearby objects clearly. Usually caused by an eyeball that is too short
Blind Spot
The optic nerve’s exit creates a gap in the visual field, “filled in” by the brain.
Rod and Cone Adaptation
Rods: Adapt to dark over ~25 minutes (higher sensitivity).
Cones: Adapt in ~3–4 minutes, plateauing sooner.
The dark adaptation curve highlights combined effects of rods and cones.
Blind Spot Demonstration
Highlights brain compensation for missing visual data.
Dark Adaptation Curve
Explores differences in sensitivity between rods and cones.
Key components of neurons
Cell body
Dendrites
Axon or nerve fiber
Sensory receptors
Specialized neurons that respond to specific kinds of energy
What do Neurotransmitters do and how are they released and accepted?
Released by the presynaptic neuron from vesicles.
Received by the postsynaptic neuron on receptor sites.
Matched, like a key to a lock, into specific receptor sites.
Used as triggers for voltage change in the postsynaptic neuron.
Modularity
The idea that specific brain areas are specialized to respond to specific types of stimuli or functions.
Distributed representation
The idea that the brain represents information in patterns distributed across the cortex, not just one brain area.
The distributed approach to representation focuses on the activity in multiple brain areas and the connections between those areas.
Electromagnetic spectrum
Energy is described by wavelength.
Spectrum ranges from short wavelength gamma rays to long wavelength radio waves.
Visible spectrum for humans ranges from 400 to 700 nanometers.
Most perceived light is reflected light
The Eye
The eye contains receptors for vision.
Light enters the eye through the pupil and is focused by the cornea and lens to a sharp image on the retina.
Rods and cones are the visual receptors in the retina that contain visual pigment.
The optic nerve carries information from the retina toward the brain.
Differences between rods and cones
Shape
Rods - large and cylindrical
Cones - small and tapered
Distribution on retina
Fovea consists solely of cones.
Peripheral retina has both rods and cones.
More rods than cones in periphery.
Refractive myopia
cornea or lens bends too much light.
Axial myopia
eyeball is too long.
Rod spectral sensitivity shows
more sensitive to short-wavelength light.
most sensitivity at 500 nm.
Cone spectral sensitivity shows
Most sensitivity at 560 nm.
Purkinje Shift
Enhanced sensitivity to short wavelengths during dark adaptation when the shift from cone to rod vision occurs
Rods and cones send signals vertically through…
Bipolar cells
Ganglion cells
Ganglion axons
Signals are sent horizontally…
Between receptors by horizontal cells
Between bipolar and between ganglion cells by amacrine cells
Three lightness perception phenomena explained by lateral inhibition
The Hermann Grid: Seeing spots at an intersection
Mach Bands: Seeing borders more sharply
Simultaneous Contrast: Seeing areas of different brightness due to adjacent areas
Mach Bands
Enhanced perception of light/dark borders
Center-Surround Antagonism
Highest response when only excitatory areas are stimulated
Fovea Focus
Only objects directly looked at project onto the cone-rich fovea for clear vision.
Neural Convergence
Higher for rods than cones (120 rods per ganglion vs. 6 cones per ganglion)
Implications:
Rods: More sensitive but less detail
Cones: Better detail but require more light
Key Cell Types in Visual Cortex
Simple Cortical Cells: Detect orientation
Complex Cortical Cells: Respond to motion and patterns
End-Stopped Cells: Detect edges and angles
Selective Adaptation
Neurons fatigue with prolonged exposure, reducing response upon re-exposure
Gratings are used to measure contrast sensitivity
Selective Rearing
Environmental stimuli influence neuron development
Ventral Pathway (What Pathway)
Object identification
Dorsal Pathway (Where Pathway)
Object location and action guidance
Pathway to the Brain
Retina →
Optic Nerve →
Lateral Geniculate Nucleus (LGN) →
Visual Cortex (V1) → Temporal and Parietal Lobes →
Frontal Lobe
Cells that are feature detectors
Simple cortical cell
Orientation tuning curve
Complex cortical cell
End-stopped cortical cell
Function of LGN (Lateral Geniculate Nucleus)
Major function of LGN is to regulate neural information from the retina to the visual cortex.
LGN cells have center-surround receptive fields.
Retinotopic map
an electron map of the retina on the cortex.
Cortical magnification
A small area of the fovea is represented by a large area on the visual cortex.
Positron emission tomography (PET)
Person is injected with a harmless radioactive tracer.
Tracer moves through bloodstream.
Monitoring the radioactivity measures blood flow.
Changes in blood flow show changes in brain activity.
Inverse Projection Problem
An image on the retina can be caused by an infinite number of objects.
Occlusion
Objects can be hidden or blurred.
Viewpoint Invariance
The ability to recognize an object regardless of the viewpoint.
Approach established by Wund
States that perceptions are created by combining elements called sensations.
Principles of Perceptual Organization
Good Continuation: Points connected in smooth curves are grouped together.
Pragnanz: Perceiving stimuli in the simplest possible form.
Similarity: Grouping similar objects together.
Proximity: Grouping nearby elements together.
Common Fate: Grouping objects moving in the same direction.
Common Region: elements in the same region tend to be grouped together
Uniform Connectedness: Connected elements perceived as a single unit.
Figure-Ground Segregat
Determining what part of the environment is the figure, so that it “stands out” from the background.
Properties of Figure and Ground
The figure is more “thinglike” and more memorable than the ground.
The figure is seen in front of the ground.
The ground is more uniform and extends behind figure.
The contour separating figure from the ground belongs to the figure (border ownership).
A scene contains
Background elements.
Objects organized in meaningful ways with each other and the background.
Difference between objects and scenes
A scene is acted within.
An object is acted upon.
Physical regularities
Regularly occurring physical properties.
Oblique effect
People perceive horizontals and verticals more easily than other orientations.
Uniform connectedness
Objects are defined by areas of the same color or texture.
Light-from-above heuristic
Light in natural environment comes from above us.
All responses are a combination of
Hits
Misses
False Alarms
Correct Rejections
Signal Detection Theory
This is a psychological and statistical framework used to explain how decisions are made under conditions of uncertainty.
You need to differentiate the difference between the signal (info your trying to detect) and the noise (all background distractions)
There are many different decison outcomes like hit, miss, false alarms and correct rejections
Influence of Payoffs
Changing incentives can shift response criteria without affecting sensitivity.
