Psychology part A, ch. 3 - Sensation and Perception

Bottom-up processing

taking sensory information and then assembling and integrating it

—>stimulus driven processing

Top-down processing

Using models, ideas, and expectations to interpret sensory information

—> conceptually driven processing

what boundaries does sensation have?

1. what is the weakest stimulus an organism can detect —> absolute threshold

what ways of measuring (psychophysics) is there to find the absolute threshold? 3

1. method of limits (ascending / descending intensities)

2. adaptive testing

3. method of the constant stimuli

treshold stimulus level

the lowest intensity level at which a stimulus is detected 50% of the time

In the method of constant stimuli detection why does detection vary? 2.5

• Mental alertness

• Internal “noise”

• Other random influences

discrimination

weakest difference between two stimuli an organism can detect

—> differnece/differential threshold or just noticeable difference (JND)

weber fraction

how is the weber fraction used in marketing

• so that negative changes (e.g., reductions in product size or quality, or increase
  in product price) are not discernible to the public (i.e., remain below JND) and

• so that product improvements (e.g., improved or updated packaging, larger size
  or lower price) are very apparent to consumers without being wastefully
  extravagant (i.e., they are at or just above the JND).
  See Digging Deeper on Toledo: Applying Weber’s law to pricing

what problem does constant stimuli not account for

response bias

response bias

Response bias is the tendency of a person to respond in a particular way regardless of the actual stimulus.

In detection experiments, it reflects a participant’s decision strategy — whether they are more likely to say:

• “Yes, I detected it” (liberal bias)

• “No, I didn’t detect it” (conservative bias)

even when the sensory evidence is uncertain.

how can we deal with response bias?

when you are more sensitive to the signal, your internal response will be stronger (larger difference between noise+signal distribution)

what does the accessory structure in the eye do?

brings energy (stimulus) to receptors for transduction

sensory adaptation

loss of responsiveness in receptor cells after
stimulation has remained unchanged for a while.

Habituation

the tendency of the brain to stop attending to constant, unchanging information

what kind of casual information does your brain care about?

contrast - the relative difference in the amount (and type of light) coming from two nearby locations

how is the contrast signal received? 5

1. light

2. photoreceptors

3. bipolar cells

4. ganglion cells

5. optic nerve

percept

• the meaningful product of (the process of) perception

• often, a stimulus that has been associated with concepts, memories of events,
  emotions, motives…

feature detection

brains detector cells respond to specific features - edges, lines, and angles

retinal processing

receptor rods and cones —> bipolar cells

—> ganglion cells

recognition

brain interprets the constructed image based on information from stored images

parallel processing

brain cell teams process combines information about color, movement, form and depth

what does the dorsal visual stream determine?

where is it?

what does the ventral visual stream determine?

what is it?

what are feature detectors?

specialised groups of cells in both pathways

feature binding problem

How does the brain combine (or ‘bind’) multiple features given that their
activation is distributed across many regions in the brain?

Gestalt theory

emphasizes how we organize incoming stimulation into meaningful perceptual patterns because of the way are brains are innately “wired”.

innate principles (“gestalt laws”) guide grouping of parts (of objects /figures) into perceptual ‘wholes’ or ‘gestalts’

figure ground

Figure–ground is the perceptual process where the visual system separates a scene into:

• Figure = the object you focus on

• Ground = the background behind it

Key idea: Your brain automatically decides what is “object” vs “background”.

common fate

Objects that move in the same direction or at the same speed are perceived as belonging together as a group.

Key idea: Motion signals grouping.

learning based inference

Learning-based inference is a concept in psychology and cognition that refers to how we use previous experience (learning) to make predictions, judgments, or interpretations about new situations.

perceptual interpretations

• inferences – guesses – predictions about meaning of sensations

• generated hypotheses about sensations
  based on learning

perceptual set

A perceptual set is a cognitive bias where perception of a stimulus is influenced by expectations, prior experience, and context, leading individuals to interpret ambiguous information in a specific way.

Muller-lyer illusion

perceptual constancies

the ability to recognize the same object under different conditions, such
as changes in illumination, distance, or location
e.g. shape constancy

multimodal perception

Multimodal perception is the brain’s ability to combine information from different sensory modalities (e.g., vision, hearing, touch) to create a single, coherent perceptual experience.

McGurk effect

What it is:
A perceptual illusion where visual information changes what you hear.

Example:

• You hear “ba”

• You see lips saying “ga”

• You perceive “da”

👉 Shows that speech perception is multisensory, not purely auditory.

Rubber hand illusion

What it is:
An illusion where people feel that a rubber hand is their own when:

• their real hand is hidden

• both the rubber hand and real hand are stroked synchronously

Result:
They experience ownership of the fake hand.

👉 Shows how the brain integrates vision + touch + proprioception to construct body ownership.