Week 1: perceptual process & Methods and Neural firing

What are the stages of how our perceptual experience is formed?

Step 1: Distal/Environmental stimulus (transformation)
Step 2: Proximal Stimulus/stimulus on the receptors (representation)
Step 3: Transduction
Step 4: Neural Processing
Step 5: Perception
Step 6: Recognition
Step 7: Action

Which steps of the perceptual process does knowledge play a role?

Processing, perception, recognition, action

What happens during transduction?

Sensory receptors transform environmental energy into electrical energy

Where within the perceptual process is knowledge integrated?

Processing, perception, recognition, action. That is why they influence each other because our past experience/prior knowledge impacts how we recognize things.

What are the three ways we can study the relationship between physical stimuli, our perception of those stimuli (behavioral), and the physiological response?

Stimulus-Behavior relationship: physical + psychological (behavioral) response

Stimulus-Physiology relationship: stimuli + physiology

Physiology-Behavior relationship: stimuli + psychological (behavioral)

How does the stimulus-behavior relationship study the relationship between the stimuli and our perception of it?

Psycho physics. Measures the relationship between the physical stimulus and the psychological response.

E.g., The oblique effect produced results arguing people see vertical/horizontal lines better than oblique lines. This was studied by measuring grating acuity (smallest line width participants can detect at different orientations)

How does the stimulus-physiology relationship study the relationship between the stimuli and physical response to it?

By measuring brain activity, such as neurons firing.

E.g., oblique effect in ferrets’ brain activity was measured using optical brain imaging, showing larger responses to horizontal and vertical orientations than to oblique ones

How does the physiology-behavior relationship work?

By relating physiological responses to behavioral responses. Researchers can measure both responses in the same participants for a direct assessment. Crucial to study alongside the influence of knowledge-based processing

E.g., for the oblique effect, fMRI was used to measure brain responses and behavioral sensitivity to gratings in the same individuals, showing greater brain responses and higher sensitivity to vertical and horizontal orientations than to oblique ones.

What are the different psycho physical methods?

Method of limits

method of adjustment

method of constant stimuli

How does the method of limits work?

Stimuli is presented in ascending or descending levels of intensity. Participants state when they can and cannot perceive stimuli.

Threshold determined by taking mean between last perceived and first unperceived stimulus.

to minimize bias, procedure is repeated multiple times with half the trials starting about the threshold and the other half starting below.

How does the method of adjustment work?

It is participant led in which they have a knob and adjust stimulus intensity continuously until they can just barely detect it.

repeated multiple times. final threshold determined by taking the average of all the participants settings

Fastest to conduct and has the most bias

How does the method of constant stimuli work?

different stimuli intensities presented one at a time in a random order. Participants stats whether they perceive it or not. Same intensities presented many times.

Threshold detected at 50% of the trials

Most accurate and minimizes the most bias

How do we rid of bias in the psychophysical methods?

Forced choice procedure which requires participants to choose an answer from a predetermined set of options even if unsure. There is two time intervals, one without stimulus.This helps control response bias. Can be combined with method of limits and constant stimuli.

E.g., “Do you see the light? Yes or No"?” turns into “Where did you see the light? Left or Right?”

Compare and contrast the main parts of a neuron

• Cell body: keeps cell alive

• Dendrites: big/short/many of them, branch out from the cell body and receives electrical signals from other neurons

• Myelin sheath: wrap around nerve fibers/axons that protects them and enables electrical impulses to transmit quickly and efficiently along the nerve cell (kind of like an electrical insulator)

• Axon: long and extends from cell body. conducts electrical signals from cell to body to other neurons

• Axon terminal: releases neurotransmitters (chemical) into synaptic cleft which transmits signals to other cells

What are the main properties of light waves and how do they affect perceptions of light?

Wavelength: affects our perception of color. short waves = blue, long waves = red

Amplitude: larger (taller) = brighter

Purity: saturation (how much achromatic light is mixed in)

What are the various parts of the eye?

• Cornea: clear part of the eye. does 70-80% of focusing. Curves light to land directly on retina
  Sclera: white part of eye. keeps it into a ball

• Pupil: opening through which light enters the eye

• Iris: the colorful ring that adjusts to let more or less light in pupil

• aqueous humor: the fluid in front of the lens

• Lens: transparent structure behind the pupil that adjusts focus to land on retina (accommodation).

• Vitreous humor: fluid behind the lens

• Retina: network of neurons lining the back of the eye, contains the photoreceptors

  • Photoreceptors: rods and cones

• Fovea: small area in the retinal that serves as the point of central focus. only contains cones

• Optic nerve: bundle of nerve fibers that leaves the back of the eye and carries signals to the brain

• Blind spot: area in the back of eye where there are no photoreceptors

What role does the different parts of the eye play in vision?

• pupil: regulates the amount of light entering the eye

• cornea: 70-80% of eye’s focusing power. fixed and cannot adjust focus

• lens: provides remaining of eye’s focusing power. can change its shape to adjust focus for objects at different distances through accomodation

• Retina: receives focused light and contains the receptors for vision, forming images of objects. processes electrical signals through a network of neurons

• Photoreceptors: contain light-sensitive visual pigments that react to light and initiate visual transduction, transforming light energy into electrical signals

• Fovea: cones only, responsible for sharp central vision and seeing fine details, used when directly looking at an object

  • optic nerve: transmits electrical signals from the retina to the brain

Why does the blind spot exist?

Exists because there a spot in the retina where there are no photoreceptors. No light-sensitive cells = no image falling on this region can be detected This occurs because its where the nerve fibers that form the optic nerve leave the eye to carry visual signals. W

Why are we not aware of the blind spot?

• location: located in the peripheral visual field, so its where objects are not in sharp focus anyway

• Brain filling in: most importantly, the brain “fills in” the missing information. Brain creates a perception that matches the surrounding pattern, making the discontinuity unnoticeable unless actively testing for it.

What is macular degeneration? cause, symptoms, fixes?

• What: destruction of the fovea and surrounding area creating a blind region in central vision

• Cause: genetic, but also exacerbated by environmental factors, most common in older people

• Symptoms: blind spot in central vision causing people to lose sight of whatever they look at directed

  • fixes: unsure

What is retinitis pigmentosa? cause, symptoms, fixes?

• What: degeneration of the retina. first begins with attack on peripheral rod receptors leading to poor vision in the peripheral visual field. In severe cases, foveal cone receptors are also attacked, resulting in complete blindness

• cause: genetics, also influenced by environmental factors

• symptoms: tunnel vision.

  • Fixes: bionic eye, partially restores vision, allowing perception of contrasting lightness vs darkness
    

What is presbyopia? causes, symptoms, fixes?

• What: hardening of the lenses and weakening of eye muscles, decreasing ability to accommodate

• Cause: age

  • Symptoms: blurry vision for close-range objects
    Fixes: reading glasses

What is myopia? causes, symptoms, fixes?

• What: parallel light rays focused in front of the retina

• Causes: lens having too much focusing power or unable to flatten enough, cornea too curved or too steep, eyeball is longer than normal

• Symptoms: blurry vision of distant objects

• Fixes: corrective lenses or surgery

what is hyperopia? causes, symptoms, fixes?

What: focusing of parallel light rays behind retina

Causes: usually eyeball is too short. Focus for distant objects is fully accommodated (maxed out) that it cannot accommodate any further for close-range objects.

Symptoms: blurry vision of close objects

Fixed: corrective lenses. young people may be able to accommodate just enough

What is astigmatism? cause, symptoms, fixes?

• what: light focuses unevenly on retina

• cause: eyeball is too long

• Symptom: blurred distorted visions of images, lights looks like bursts of light

• fixes: corrective lenses

What are cataracts? causes, symptoms, fixes

• what: clouding of the eye’s

• causes: aging, proteins in lens break down and clump together. diabetes/high blood pressure can increase risk

• symptoms: blurred/cloudy vision. difficulty seeing in dim light

• fixes: surgery to replace lens with artificial one. must wear corrective lenses after.

What is glaucoma? causes, symptoms, fixes

• what: damage of the optic nerve

• causes: poor drainage of aqueous humor, due to clogging, causing fluid build up and pressure on the optic nerve. causes nerve death

• symptoms: gradual loss of peripheral vision, blurred vision

• fixes: no cure, treatment can help slow its progression.

What are the two types of receptors in the retina? Explain their differences

• Rods: rod-like shaped, particularly in periphery. more rods than cones

  • achromatic, responsible for low-light vision and detecting shades of gray. highly sensitive to light

  • higher convergence = lower spatial resolution

    • many rods synapse onto one single ganglion cell

  • one visual pigment absorbing best at 500 nm

• Cones: cone-shaped, concentrated in fovea.

  • 3 visual pigments for color perception, responsible for bright-light vision, sharper vision (better acuity)

  • lower convergence

    • fewer cones synapse onto a ganglion cell

  • faster temporal resolution

How do receptors transduce light into electrical energy?

Occurs in the rods and cones

• Photoreceptors made up of opsin and retinal (smaller light-sensitive component)

• Incoming light hits retinal, causing retinal molecule to change its shape (isomerization)

• ismerization triggers chemical chain reaction activating thousands of charged molecules creating electrical signals in the receptors

• Electrical signals processed by the brain.

• Visual pigment (aka retinal) must regenerate to its original shape and reattach to opsin to be able to signal light again

Why does the dark adaptation curve have such a funky shape?

Because it shows two distinct phases:

1. Cone adaptation, initial rapid phase: in the first few minutes after lights are turned off, cones increase sensitivity rapidly and reach max sensitivity. (observed when light hits cone-rich fovea)

2. Rod adaptation (later slower phase): rods continue to adapt slowly. after about 7 mins in the dark, rods’ sensitivity surpasses that of the cones, becoming the dominant mechanism for vision in dim light, and their sensitivity continues to increase for 20-30 mins until it reaches its max

3. Rod-cone break is where there’s a switch between cone to rod, cone reaches maximum, sensitivity, rods are still increasing sensitivity

What is the Purkinje Shift? Why does it happen?

• What: enhanced perception of short-wavelength light (blue/green) that occurs during dark adaptation

• Why: vision transitions form cone-dominated to rod-dominated vision. Rods are most sensitive to light of 500nm whereas cones are most sensitive to light of 560nm.

• Difference in spectral sensitivity between rods and cones causes the shift in perceived brightness towards blue and green hues as we adapt to darkness