ch. 1 intro to perception

what does the grading acuity experiment measure

what does the grading acuity experiment measure

the absolute threshold for seeing fine lines

what is the absolute threshold

the smallest stimulus level that can just be detected (i.e. the smallest line width in the grating acuity experiment)

what is an example of absolute threshold using the sense of hearing and taste

• hearing: the smallest amount of salt you need to taste it

• hearing: the intensity a whisper needs to be for you to just barely hear it

what is a threshold

measures the limits of sensory systems (the minimums)

what were the beliefs about the mind and body in the 1800s

• mind and body as totally separate

• body=physical (could be seen, measured, studied)

• mind= not physical, invisible (not measurable, or studied)

who is Fechner and what were his beliefs about the mind and the body?

• physics professor who measured diff ways of studying threshold

• mind and body should not be thought of as separate from one another but as two sides of a single reality

• most importantly, mind could be studied measuring the relationship between changes in physical stimulation (body) and a person’s experience (mind)

• + physical stimulation=+ person's perception of stimulus (i.e. by increasing the intensity of a light, the person's perception of the brightness of the light also increases)

what are the 3 ways of measuring threshold (classical psychophysical methods)

elements of psychophyics:

1. method of limits

2. method of constant stimuli

3. method of adjustment

what is the method of limits

experimenter presents stimuli in either ascending order (intensity is increased) or descending order (intensity is decreased) and participant responds yes or no

• ex. how loud do tones of different frequencies have to be before you detect them (i.e. the absolute frequency)

method of constant stimuli

• similar to method of limits (stimulus presented one at a time + participant responds yes/ no on each trial)

• difference is that simulus is presented in a random order rather that + or -

what is method of adjustment

the participant adjusts the stimulus intensity until they can just barely detect it

• faster bc participants can determine threshold in a few trials

what is the difference threshold

the smallest difference between two stimuli that enables us to tell the difference between the reference and comparison stimulus (ex. weight)

• Webster measured difference threshold between stimuli

  • it is always proportional to the reference stimulus for different stimuli (i.e. electric shock comparison has to be 1% different than the reference stimulus, and so on)

what is a perceptron (Rosenblatt)?

Computer that teaches itself to distinguish between basic images (i.e. cards with markings on left and right)

• detect similarities and diffs between patterns, of optical, electrical, or tonal information in a manner that is similar to perceptual processes of the biological brain

what is the “computer’s problem”?

that the computer doesn’t have a huge store-house of information that humans accumulate when we are born

what were scientist’s common misconception of perception?

that they could easily create a computer capable of human-like perception, and that perception was easy to create

what are some medical devices that depend on perception?

• devices that allow people to restore perception (vision, hearing, pain treatments)

• autonomous vehicles (i.e. tesla)

• face recognition systems

• speech recognition systems

• highway signs (visible in different conditions)

What does perception greatly depend on?

the properties of sensory receptors

the difference between sensation and perception:

• sensation: involves elementary processes that occur at the beginning of the sensory system

• perception: complex processes that involve higher-order mechanisms (i.e. interpretation and memory)

  • ex. dots analysis experiment: seeing three dots as forming a triangle

Describe the steps of the perceptual process:

1. stimulus in environment

2. stimulus hits receptors

3. receptors process

4. neural processing

5. perception

6. recognition

7. action

explain distal and proximal stimuli (step 1 and 2).

1. info about the distal stimulus (out in the environment) is carried by light (ex. light reflection from a tree entering the eye and reaching visual receptors)

2. light is transformed into electrical energy when it is reflected from the stimulus (ex. tree). The result is the proximal stimulus: the image of the tree on the retina (close to receptors)

   (ex. air pressure→ rustling of leaves enter the ear and reach auditory receptors)

**distinction between the 2 illustrates transformation and representation. Distal stimulus is transformed into proximal

what is the principle of transformation?

stimuli and responses created by stimuli are transformed or changed between the distal stimulus (environmental) and perception

what is the principle of representation?

everything a person perceives is based on representations of stimuli that are formed on the receptors and resulting activity in the person’s nervous system

describe the receptor process (step 3)

photoreceptors (rods and cones):

1. visual pigment reacts to the light and transform environmental energy into electrical energy→ nerve impulses (i.e. transduction)

2. end result= electrical representation of stimulus (i.e. tree)

describe the neural processing (step 4)

neural processing: changes that occur as signals are transmitted through the maze of neurons

neurons:

1. transmit signals from the receptors to the brain and then within the brain

2. change (or process) these signals as they are transmitted (neural processing)

   • signals are reduced or amplified to have added strength when they arrive at the brain (cerebral cortex)

• primary receiving areas of the brain: occipital lobe, temporal lobe, parietal lobe (somatosensory)

frontal lobe

receives signals from all the senses and plays an important role in perceptions that involve the coordination of info received through two or more senses

explain the behavioural responses (steps 5-7)

• electrical signals are transformed into conscious experience that person can perceive and recognize

• perception: conscious awareness of the stimuli (i.e. tree)

• recognition: placing an object in a category (i.e. tree) which gives it meaning

• action: motor activities in response to the stimulus (i.e.taking action when moving eyes and head to look at different parts of the tree)

Sacks (1985) The man who mistook his wife for a hat

• Dr. P., a music teacher had trouble recognizing his students but could recognize their voices

• he began misperceiving common objects (ex. expecting doorknob to engage in conversation)

• diagnosed with visual form agnosia: inability to recognize objects

• couldn’t identify the whole object

• could recognize parts of the object, but he couldn’t perceptually assemble the parts to recognize object as a whole

Milner and Goodale (1995) evolutionary purpose of perception

to help the animal control navigation, catch prey, avoid obstacles, detect predators (crucial to their survival)

rat-man demonstation

shows how recently acquired knowledge (being told it is a rat) can influence perception

bottom-up vs. top-down processing

• bottom-up: based on incoming stimuli from the environment (data-based)

• top-down: based on perceiver’s prior knowledge or experience (knowledge-based)

what are the 3 relationships in the perceptual process?

1. stimulus-behaviour or perception (ex. pressure on shoulder= feeling it and reacting to it)

2. stimulus-physiology (ex. pressure on shoulder leads to neural firing)

3. physiology-behaviour or perception (ex. neural firing = feeling on shoulder)

1. stimulus-behaviour

relates stimuli to behaviours like perception, recognition and action (steps 5-7)

• can be measured using psychophysics: measures relationship between physical and psychological (ex. the oblique effect)

oblique effect (1)

• presented black and white striped stimuli called gratings and measured grating acuity (the smallest width of lines that participants can detect)→ gets thinner and thinner

• results show that grating acuity is best for gratings oriented vertically and horizontally rather than obliquely

• stimulus: oriented gratings

• response: detecting the grating’s orientation

**example of using psychophysics

2. stimulus-physiology

relationship between stimuli and physiological responses like neural firing (steps 1-2)

• often studied by measuring brain activity with optical imaging

  (ex. oblique effect on ferrets)

Coppola et al., 1998 oblique effect on ferrets

• presented lines of diff orientations to ferrets

• optical brain imaging showed more activity in visual brain regions when ferrets looked at lines that were horizontal or vertical compared to oblique

** stimulus-physiology

3. physiology-behaviour

relates physiological responses and behavioural responses (steps 3-4)

• use fMRI

Furmanski and Engel (2000) brain response and behavioural sensitivity to grating orientations

• decreased intensity between light and dark bars until the participant can no longer detect the orientation of the bars

• able to detect orientation of light-dark differences for vertical and horizontal bars more than for oblique

  • more sensitive to vert and horz

• fMRI showed larger brain responses to vertical and horizontal lines than to oblique

**physiology-behaviour

magnitude estimation

determining the relationship between physical stimuli and the perception of their magnitude (stimulus-behaviour)

ex. participant is asked to use numbers to represent the loudness of a stimulus from 1-20

• perceived magnitude: rating of loudness compared to original sound

• change in intensity results in same change in magnitude

  • as shock gets more intense, you can change it by less and the person will feel it getting more intense

    • (expansion: change in magnitude estimation is not corresponding to the stimulus intensity)

Questions to ask in order to measure perception

1. what is the perceptual magnitude of the stimulus

2. what is the identity of the stimulus (recognition testing)

   • test ppl with brain damage and compare to those without

3. How quickly can I react to it (reaction time)

4. how can i describe what is out there (i.e. phenomenological report)

5. how can i interact with it

How is perception of light measured?

1. perceived brightness (not intensity)

2. electromagnetic spectrum

optical imaging

electrical activity of neurons is related to local metabolic activity and blood flow (higher metabolism when area is used more)

• used to measure the stimulus-physiology relationship

• correlates of brain activity:

  • blood volume changes

  • blood oxygenation changes

  • light scattering changes caused by ion and water movement