Sensation and Perception Exam 1

Sensation

Raw data processed by sensory receptors (eyes, nose, ears, etc.)

Perception

Sensations are processed by the brain (makes meaning out of perceptions)

Why study perception?

It is a multi disciplinary field that has broad applications and implications for science, technology, medicine, education, and life

• Improving AI

  • Insights from human perceptions can inform the development of more human-like intelligence systems (bionic eyes and self-driving cars)

• Enhancing Clinical Practices

  • Leads to better diagnosis and treatment of perceptual disorders (visual impairment, auditory processing, etc.)

• Exploring Consciousness

  • Perception is closely linked to consciousness

  • Studying perception can shed light on the nature of conscious experience and the mechanisms underlying awareness

Cranial Nerves

Transmit neural activity from sensory organs to the central nervous system (i.e., the brain)

- Auditory nerve, optical nerve, etc.

Johannes Muller

• Doctrine of Specific Nerve Energy

  • Perception is determined by which sensory nerve is stimulated, rather than the specific type of stimulus (e.g., light, sound, pressure) that triggers the nerve

Wilder Penfield

• Montreal Neurological Institute

  • Electronically stimulated different portions of the cerebral cortex on awake (local anesthesia) patients to map different areas of the brain and understand their functions

  • How different regions of the cortex contribute to sensory perception, motor control, and various cognitive processes

  • MNI Brain - anatomical reference for brain structures

Santiago Ramon y Cajal

Made detailed drawings of nerve cells/ neurons and provided evidence that the nervous system was comprised of single cells

Otto Loewi

Showed that transmission between neurons at the synapse involves the release of chemicals called “neurotransmitters” 

Brain

• Contains specialized pathways for each of the senses

  • Some areas process info from only one sense (primary visual, auditory, somatosensory)

  • Some areas integrate info from multiple senses (thalamus (all except smell), superior temporal gyrus (auditory and vision)

Neurons

Fundamental building blocks of the nervous system. They are specialized cells responsible for transmitting information throughout the brain and body

Steps of the Perceptual Process

• Environmental stimulus

• Sensory receptors

• Receptor process

• Neural processing

• Perception

• Recognition

• Action

Principle of Transformation

Stimuli and responses created by stimuli are transformed, or changed, between the distal stimulus (in the environment) and perception

Principle of Representation

Everything a person perceives is based not on direct contact with the stimuli but on representations of stimuli that are formed on the receptors and the resulting activity in the person’s nervous system

Transduction

Transformation of environmental energy (e.g., light, sound, energy) to electrical energy

Sensory Receptors

Cells specialized to respond to environmental energy

Top-Down Processing

• Based on knowledge (previous experience)

  • Memory, expectations, knowledge about the nature of the stimulus

  • Select and examine features

  • Recognize stimulus

• When a person has previous knowledge or experience and uses that to recognize a stimulus

Bottom-Up Processing

• Based on incoming data that stimulates your response

  • Sensory receptors, detect specific feature of the stimulus

  • Combine features

  • Recognize stimulus

• When receptors are stimulated by new data and using that data to create a recognizable stimulus without previous knowledge

Classical Methods to Measure Threshold (Gustave Fechner)

• Method of limits

• Method of Constant Stimuli

• Method of Adjustment

Method of Limits

How is it done: the experimenter presents stimuli in either scending order (intensity is increased) or descending order (intensity decrease) - observer responds whether stimulus is perceived

Threshold: average of all crossover points

Advantage/Disadvantage: More efficient; has issues (subject anticipation)

Method of Constant Stimuli

How is it done: Different stimulus intensities are presented at one time, and the participant must respond whether they perceive it (same as method of limits), but the stimulus intensities are presented at random (rarely to almost always perceivable). The participant with respond yes/no or same/different

Threshold: the intensity that results in detection on 50% of trials

Advantage/Disadvantage: Most accurate (many observations and stimuli randomly presented); Time consuming

Method of Adjustments

How is it done: the participant adjusts the stimulus intensity continuously until they can just barely detect the stimulus

Threshold: taking the average setting

Advantages/Disadvantages: Few trials needed for observer to find their own threshold; faster; Subject anticipation

Above Threshold Measurement

• Magnitude Estimates

• Recognition Testing

• Reaction Time

• Phenomenological Report

Magnitude Estimation

• Used to describe the relationship or mapping between the physical stimulus intensity and the magnitude of the perceptual experience

What is the procedure: the participant assigns values according to perceived magnitudes of stimulus

Response Compression: strength of the stimulus increases, so does the perception, but perception does not have a 1-to-1 relationship with stimulus increasing

Recognition Testing

• Identifying or categorizing things

  • Used to assess brain damage and perceptual abilities

One thing we have learned from perception through recognition testing is that some things we perceive really fast but some details take longer

Reaction Time

Time between the perception of a stimulus and the person’s reaction to it

Phenomenological Report

• This is our subjective experience of stimulus

• Allows us to understand perceptions

Neuron Anatomy

KNOW THE LOCATIONS OF THE PARTS

Soma

Cell nucleus (control center) integrates the information received from all other cells

Dendrites

Where the neuron receives the information from other neurons (a neuron can have many dendrite branches)

Axon

Long, thick fibers where the information that is being sent travels along

Terminal Buttons

Terminals at the end of the axon that sends the neurotransmitters to other cells’ dendrites when activated

Neurotransmitters

Chemical messengers are stored in synaptic vesicles (2 types: excitatory, inhibitory)

Synapse

Space between neurons

How do Researchers Measure APs?

• Action/Membrane Potential: difference in electric potential between the interior and the exterior of the biological cell

• Small electrodes are used to record from single neurons

Resting State

• The difference between the recording electrode (inside nerve fiber) and reference (outside) is calculated

• This negative charge of the neuron relative to its surroundings

  • Difference between inside and outside is -70 mV

Threshold for Firing an AP

Minimum potential difference threshold must be reached in order to fire an AP

- For most neurons in humans, this lies around ~ -50mV and -55mV

Depolarization

• Electrically: The cell’s voltage becomes more positive (+)

• Chemically: Influx of positive sodium ions

Repolarization

• Electrically: Around +40, the voltage becomes more negative (-)

• Chemically: the cells returns to its resting state as potassium comes in

Refractory Period

• Electrically: A neuron can’t fire a new action potential

• Chemically: Sodium channel gates close and potassium gates open

Synaptic Transmission

• Excitatory Transmitters: causes depolarization

  • Neuron becomes more positive (+)

  • Increases the likelihood of an AP

• Inhibitory Transmitters: causes hyperpolarization

  • Neuron becomes more negative (-)

  • Decreases the likelihood of an AP

Basic Properties of Action Potentials

• Show propagated response: Once a response is triggered, it travels all the way down the axon without decreasing in size

• All or nothing theory: an AP in a neuron will either occur fully or not at all, regardless of the strength of the stimulus

  • Increase in stimulus intensity results in an increase in rate of firing 

Specificity Coding

• A specialized neuron that responds only to one concept or one complex stimulus (also known as grandmother cells)

• Quian Quiroga’s study provided evidence for this concept

  • Put 440 microelectrodes in 5 epilepsy patients

  • Recorded activity of single neurons

• Major limitations of supporting research

  • Biologically limited: we only have so many cells, it would simply be impossible to have a cell for every concept

  • Research limitations: limited by the short recording time; with more time and materials, the neurons would likely respond to additional stimuli

Sparse Coding

• A particular stimulus is represented by a pattern of firing of only a small group of neurons (most neurons remain silent)

• Evidence that the code for representing objects, tones, and odors may involve a pattern of activity across a relatively small number of neurons

• Advantages: Efficient - fewer neurons are active

• Weaknesses: Not robust

Population Coding

• Proposes that our experiences are represented by the pattern of firing across a large number of neurons

• A large number of stimuli can be represented, because large groups of neurons can create a huge number of different patterns

• Advantages: Robust: because information is distributed across many neurons, the system is less likely to lose information due tot damage or noise in individual neurons

• Weaknesses: Takes up a lot of energy or capacity

Representations

• Modulatory

• Distributed

• Connectivity

Modulatory or Modular Organization

• The idea that specific brain areas (modules) are specialized to respond to specific types of stimuli or functions

• One way to know the function of a brain region is to essentially turn it off and see what happens (Transcranial Magnetic Stimulation - TMS)

  • The Broca’s area is crucial for the production of speech and the Wernicke’s area is crucial for language comprehension

Distributed

• The idea that the brain represents information in patterns distributed across the cortex, not just one brain area

• This approach to representation focuses on the activity in multiple brain areas and the connections between those areas

Structural Connectivity

The anatomical organization of the brain through white matter tracts that connect cortical and subcortical regions (Taken with MRI - give structures)

Functional Connectivity

A measure of how brain regions interact with each other, even if they aren’t directly connected by white matter tracts (taken with fMRI - brain activity tracked with blood flow)

Resting State (Connectivity)

An fMRI measure when the brain is not involved in a specific task

How does measuring functional connectivity help us to understand perception?

It helps describe how different brain regions communicate and work together when making perceptions

Light

Electromagnetic radiation that travels in waves

Amplitude

Height of the wave

Wavelength

Distance between peaks

Eye Structure

KNOW THIS STUFF

Pupil

Dark circular opening at the center of the iris in the eye, where light enters the eye

- Change size to allow more or less light; also change due to mental activity or drugs

Cornea

The transparent “window” into the eyeball also involved in focusing light on to the retina

Lens

The lens inside the eye, which focuses light onto the back of the eye

- Accommodation: process of lens changing size (object near - lens fat; object far - lens skinny)

Retina

A light sensitive membrane in the back of the eye that contains rods and cones (sensory receptors)

- The lends focuses an image on the retina, which then sends signals to the brain through the optic nerve (transduction occurs before sending signals)

Rods

Receptor better for vision in low light and peripheral vision (~120 million)

Cones

Vision in high light and color detailed vision (~6 million)

Fovea

Area that only contains cone receptors (point of central focus)

Peripheral Retina

Outside of the fovea; has both rods and cones (majority rods)

Optic Nerve

Nerve fiber transmitting impulses to the brain from the retina at the back of the eye (first to thalamus)

Optic Disc

Where the optic nerve exits the retina

Blind Spot

A small area at the back of the eye, where there are no visual receptors, so images that fall directly on the blind spot cannot be seen

Macular Degeneration

Damage of the macula (aka fovea), creating a central blind spot

Retinitis Pigmentosa

First damages the peripheral rod receptors (progressive genetic disorder)

Visual Transduction

When light energy is transformed into electrical signals

Dark Adaptation

• Increasing sensitivity to the dark

• Takes 30-40 minutes to adapt to the dark

• Pupil size gets larger in short amount of time

• The threshold decreases over time, meaning that the eye can detect progressively dimmer light as it adapts

How to Measure Dark Adaptation

1. Exposed to light = Light Adaptation - expose the subject to a bright light for a set period (5-10 minutes)

- Bleaches the photopigments in the retina, maximizing the contrast when moving to darkness

2. Darkness - Turn off the light source

3. Immediately begin recording the subjects’ ability to detect a dim light stimulus over time (presented at regular intervals)

4. Look at fixation point - Test light flashes to the side - peripheral retina with rods and cones

5. Methos of adjustment - adjusts the knob until it can be barely seen to measure threshold and sensitivity (when threshold is high then sensitivity is low)

Sensitivity

Low - reduced ability to detect light aka not great vision in dark

High - better ability to detect light aka good vision in dark

How can we measure the pure cone curve vs the pure rod curve?

• Pure cone curve (test light only falls on the fovea)

  • Controls our vision in early stages, first 5 minutes or so

• Pure rod curve

  • After 20-30 minutes rods reach their maximum sensitivity

Rod Monochromats

People with no cones (just rods)

Rod-Cone Break (2 stages)

• Cones dominate the convo for about 5 minutes then petter out

• Rods were there all along, but become more talkative at about 7 minutes

Opsin

Long/large protein

Retinal

A small molecule which fits into the binding site of a large protein called opsin

Isomerization

Changing of shape of the retinal when it absorbs photons of light

- The chemical basis of visual phototransduction - light detection

Visual Pigment Bleaching

• Retinal molecules isomerize when they absorb light

• It no longer fits into opsin, so they separate

Visual Pigment Regeneration

• Retinal and opsin must recombine to respond to light

  • Cone pigment regenerates in 6 minutes

  • Rod pigment regenerates in over 30 minutes

How does Information from the Eye Flow to Various Parts of the Brain?

• Visual receptors (rods and cones) in the retina trigger the firing of neural signals

• Then sends impulses along the optic nerve (a collection of axons that connect the eye with the brain)

Optic Chiasm

The point at which axons from the inside half of each eye cross over and project to the opposite side

Lateral Geniculate Nucleus (LGN)

• It sorts visual inputs and performs basic visual processing - it regulates neural information

• Sends information to primary visual cortex and superior colliculus (important for controlling movement of the eyes)

Feedback Loops

• Involve information flowing back from the visual cortex to the LGN

• Allows for more complex, top-down processing where higher order brain regions influence earlier stages of visual processing

Primary Visual Cortex (V1)

First hits the primary visual cortex (v1) or the striate cortex in the occipital lobe

• V1 has 6 layers that process depth perception, color, form, and motion

Hubel and Wiesel (1965)

Made substantial contributions to the study of receptive fields. They projected stimuli onto a screen and had anesthetized animals, usually a cat or monkey, look at the screen with glasses so the stimuli would be in focus on the back of the eye.

Receptive Field

A specific region of sensory space where a stimulus will elicit a response from a receptor (represents the area of input that the neuron is “sensitive” to

Types of Feature Detectors

• Simple Cortical Cells

• Complex Cortical Cells

• End-Stopped Cortical Cells

Simple Cortical Cells

• In the striate cortex (V1) receptive fields are side by side with excitatory (+) and inhibitory areas (-)

• This cell likes horizontal bars, indicated by the high firing rate (an example)

• These cells are tuned to bars in particular orientations

• Finding the tuning of simple cells with orientation tuning curve - shows relationship between orientation and firing

Complex Cortical Cells

• Like simple cells, respond best to particular orientation, BUT they only respond to a bar of light if it is moving across the receptive field

• Often they will respond best to a particular Direction of Movement

End-Stopped Cortical Cells

Responds to corners, angles, or bars of a particular length moving in a particular direction

Selective Adaptation

• Refers to when firing causes neurons to become fatigued (adapted)

• Selective adaptation results in 2 physiological effects:

  • Firing rate decreases overtime

  • Firing rate is decreased when a particular stimulus immediately reappears

Selective Adaptation Procedure

Measure contrast threshold. Then view high contrast image (adapting stimulus) before measuring contrast threshold again

Selective Adaptation Results

The contrast in the repeated image should be more difficult to view than the non-repeated(in a different orientation)

Selective Adaptation - Why does this happen and what does it teach us about feature detectors?

• The neurons become less sensitive making it difficult to perceive repeated stimuli in the same grating but doesn’t impact others as much

• It teaches us that feature detectors adapting created a perceptual deficit

Selective Rearing

A procedure in which animals are raised in a special environment

• Look at how the environment (IV) impacts behavior and brain functioning (DV)

• Early environment exposure can shape neuronal functioning, like feature detectors (neural plasticity and experience-dependent plasticity)

Neural Plasticity

The brain changes and is adaptable. It forms new pathways depending on experience

Blackmore and Cooper (1970)

• Raised cats in rooms with only vertical or horizontal stripes for 5 hours a day

• Behavior

  • After 5months - visually impaired, the cats didn’t have grasping or startle reflexes

  • Vertical cats ignored horizontal things

• Brain Scans

  • The horizontal brains didn’t respond to lines within 20 degrees of vertical line

• Conclusions

  • Evidence of experience dependent plasticity, that the environment influenced the neurons

  • Connected feature detectors to perception

What/Where Pathway

What

• Ventral Pathway

• Object identification; helps with recognition of what things are

Where

• Dorsal Pathway

• Object spatial location; helps with guided behaviors

Both

• Originate in retina

• Have some interconnections

• Receive feedback from higher brain areas

Ungerleider and Mishkin Experiment

1. Object discrimination problem - a monkey is trained to pick a particular object

2. Landmark discrimination problem - the monkey is trained to pick a location

• Part of a monkey’s brain was removed

  • Removal of temporal lobe tissue → problems with the object discrimination task → what pathway

  • Removal of parietal lobe tissue → problems with the landmark discrimination task → where pathway