3. Sensation and Perception

Veridical?

Is perception _________?

• Does our perception perfectly match reality?

• We often perceive things that do not exist

• We misperceive or even fail to perceive things that do exist

• Perception does not provide an exact picture or representation of reality

We look, but don’t see!

• Ex: The Door study (link in powerpoint)

Sensation

________________ - The reception of stimulation from the environment, and its initial encoding into the nervous system.

• All sensory info is a physical characteristic of the world

  • Ex: Colors of my Playboy blanket, the speaker and sound waves vibrating and hitting the eardrums

Perception

______________ - The process of interpreting and understanding sensory information.

• Not necessarily physical

  • Ex: The implications of having a PLAYBOY blanket (am I promiscuous, what are societal implications etc.…)

Vision

Don’t worry about details, most important is the pupil, retina (contains the rods and cones)

______ - Light is reflected off the many cells at the back of the eye

• Many-to-one synapses compress information

• Peripheral rods and cones to bipolar cells

• Bipolar to Ganglion cells

Visual pathways

Ipsilateral and contralateral sides

Visual compression

________________ - Transformation of information that both analyzes and summarizes the original sensory input

• Applies to all senses (including vision)

• Summarized record of stimulus

Saccades

Gathering visual info

____________ - eyes sweep from one point to another in fast (jerky) movements

• Eye does NOT encode visual info

Fixations

Gathering visual info

___________ - The pause during which the eye is almost stationary and is taking in visual information

• Info is TAKEN IN

Change blindness

Gathering visual info

________________ - Failure to notice changes in visual stimuli when those changes occur during a saccade

• People often fail to notice changes in a visual scene

• Video in the powerpoint

Measuring eye movements

Gathering visual info

______________ - Eye trackers have been used to measure the movements of the eye.

Areas of Research:

• Perception

• Attention

• Processing facial features

• Reading

Eye Trackers:

• Light source (infrared)

• Camera/sensor

Visual attention

Gathering visual info

_______________ - The act of attending to some stimulus with our visual system

• Capacity problem

  • Select relevant information

  • Filter out irrelevant information

• Competition for said _______

  • Must be interruptible, but not too interruptible.

Inattention blindness

Gathering visual info → visual attention

_________________ - we sometimes fail to see an object we are looking at directly because attention is directed elsewhere

Ionic memory/visual sensory memory

Two names of sensory memory

______________ - Temporary visual buffer that holds visual information for brief periods of time (250–500 ms)

• The visual sensory register

Visual persistence

Visual sensory memory (ionic memory)

________________ - apparent persistence of a visual stimulus beyond its physical duration.

• Ex: Lightning strikes, or when you stare at a letter on your phone too long…

Initial storage and duration of VSM

Ionic/visual sensory memory

__________________ - At first— 250-500 milliseconds, operates without conscious awareness

• Sperling conducted several studies aimed at detailing the amount of storage in and duration of iconic memory

  • Tachistoscope

Sperling’s experiment

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration

_____________ - results of these experiments suggested that the human visual system is capable of retaining information even if the exposure is very brief. The reason so few letters could be recalled,

• Because this type of memory is so fleeting.

  • Whole Report Condition: participants had to free recall the letters (Recall as many as they could from the whole array)

  • Partial Report Condition: participants were cued to recall either the top, middle, or bottom row of the array.

Whole report condition

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration → Sperling’s experiment

_____________ - participants had to free recall the letters. They recalled 37% accurately, 4-5 items on avg. (Recall as many as they could from the whole array)

• Varying visual exposure (letter array) from 5-500 ms did not change results

• Shorter delay periods before the tone cue led to more accuracy

• Span of apprehension

Partial report condition

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration → Sperling’s experiment

______________ - participants were cued to recall either the top, middle, or bottom row of the array — recall accuracy was 76%.

Infer that ANY row would have been the same

• High tone – top row

• Medium tone – middle row

• Low tone – bottom row

Span of apprehension

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration → Sperling’s experiment → whole report condition results

_____________ - the number of items recallable after any short display

…very short

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration → Sperling’s experiment → results

Visual sensory memory (VSM)/Ionic memory is…. _______________

Decay

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration → Sperling’s experiment → results

______________ - caused forgetting, which was caused by loss of info over time.

Carefully controlled by interference.

• Sperling argued for decay because the sensory memory for the visual stimulus seemed to fade

Problem: Ecological validity

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → initial storage and duration → Sperling’s experiment → results

____________ - The extent to which findings can be generalized to real world settings in which people think and act

Interference

IMPORTANT FOR MIDTERM

Ionic/visual sensory memory → forgetting (Averbach & Coriell)

_______________ - a memory phenomenon that occurs when new information is confused with old information, making it harder to remember things

Averbach & Coriell demonstrated interference

• The idea that later stimuli replace a previous stimulus in sensory memory, thus preventing encoding, and thus memory.

Backward masking

Ionic/visual sensory memory → interference (Averbach & Coriell)

_______________ - When a later visual stimulus affects perception of an earlier one

Icon

The early parts of a fixation

___________ - the visual image that resides in iconic memory— the contents of iconic memory, quickly lost

Rayner et al. (1981) → Eye-tracker study - People fixated on a word for 50 ms, then word was replaced by irrelevant stimulus for 175 ms.

• Reading unaffected; some people didn’t notice the change!

Pattern recognition

________________ - Not instant, although sometimes very fast. Automatic & spontaneous

Principles and Models of Pattern Recognition:

• Gestalt Grouping Principles

• Template Approach

• Feature Detection

• Conceptually-Driven Pattern Recognition

Gestalt theory

Pattern recognition

______________ - Focused on the whole rather than the individual parts

• Descriptive, not explanatory

• Principle of Simplicity

Principle of Simplicity

Pattern recognition → Gestalt Theory

______________ - when we have sensory input our perceptual system usually tries to create a percept that is:

• Simple

• Orderly

• Stable

Law of proximity

Pattern recognition → Gestalt Theory

_____________ - Objects which are close together form a group

Law of similarity

Pattern recognition → Gestalt Theory

____________ - Similar visual elements form a group

• i.e., similar things are grouped together

  • Shape, colour, etc.

Law of closure

Pattern recognition → Gestalt Theory

____________ - Objects are perceived as whole, even if they are not complete

Law of good continuation

Pattern recognition → Gestalt Theory

_____________ - We tend to perceive objects as forming smooth continuous patters.

• A.K.A. Law of Continuity

Law of symmetry

Pattern recognition → Gestalt Theory

________________ - Objects that are around a center point form a group

Law of figure-ground segregation

Pattern recognition → Gestalt Theory

_________________ - Tendency to structure the visual field into two parts: a figure and a background

• Bistable percepts: stimuli can be perceived in one of two different ways.

Template approach

Pattern recognition

________________ - Patterns are not identical from one time to another

• Categorization by templates: Stored models of all categorizable patterns

• Problems: Variability of patterns that we can recognize, learning

Feature detection

Pattern recognition

_____________- appear in combinations

• Ex: “A H L T” all have a horizontal line as a feature: —

Perceptual system matches elemental features, rather than matching patterns to templates

Pandemonium model

IMPORTANT FOR MIDTERM

Pattern recognition → feature recognition

_________________ - NOT a connectionist model . On exams will be asked to explain connectionism– do NOT use this as an example

• Data/image demons: taking IN the info

• Computational demons: Different patterns have different combinations or overlapping combos – the “demons” yell out, “hey I have a match!”

• Cognitive demons: looking for EXACT matches in the full pattern- the “loudest” one is the one who has the closest match

Pros of Pandemonium model

IMPORTANT FOR MIDTERM

Pattern recognition → feature recognition → pandemonium model

______________

• Neurological evidence -> we do recognize patterns in basic features

• Parallel Processing -> multiple things happening at once in this model

• Perception is a process of problem-solving

  • Note: Doesn’t mean it’s a logical process (Like math), but it’s working with partial, incomplete info

Cons of Pandemonium model

IMPORTANT FOR MIDTERM

Pattern recognition → feature recognition → pandemonium model

_________________

• Bottom-up processing system

• No explanation for top-down effects -> for ambiguous stimulus (like certain fonts) we are using our existing knowledge/context in the environment to make connections

Conceptually-driven processing

Pattern recognition

________________ - AKA top-down processing, context and higher-level knowledge influence lower-level processes

• Pre-existing knowledge influences our perceptions. In pic– event and went are the EXACT same image with the same features, only explained by top-down processing

Data-driven processing

Pattern recognition

_____________________ - AKA bottom-up processing— processing is driven by the stimulus pattern—the incoming data (especially the features)

• E.g., Pandemonium Model

Connectionism

__________________ - theoretical and computational approach used to understand the ways in which human cognition might perform its mental operations.

A representation of how we think

• Connections are pathways between units

  • Within and between levels.

  • Massively interconnected

• Model resembles the way the brain operate

Connectionism basics

ON EXAM

Connectionism/connectionist modelling

1. Complex mental operations are the combined effects of massive parallel processing

   1. Parallel Distributed Processing (PDP) models

2. Networks are composed of three levels of units

   1. Input units: Basic units that receive inputs from the environment
        Ex: Basic visual detectors

   2. Hidden units: Internal units; one step removed from input and output

      1. Ex: Things we cant see as clearly- info from top level to guide what we don’t get

   3. Output units: Units that report the system’s response

3. Connections between units are positive or negative

   1. Positive connection weights pass excitatory message to the connected unit.

   2. Negative connection weights pass inhibitory message to the connected unit

      1. NOT action potential’s “all or nothing”

4. Connection weights vary as a function of “training” (learning algorithms)

5. Connectionism is meant to be similar to how the brain functions

   1. Still not exactly the same, nodes aren’t the same as neurons– neurons aren’t for each word or letter

Connectionism example

Connectionism

____________________ - Moreso represents nonconscious processes

• A stronger weight->  +0.9 as it FITS the Q (excitatory)

Top-down knowledge can affect the “hidden units” stage, also affected by parallel processes. If you have ST_Y recognized, you will fill in the blanks– its likely a vowel for the word to make sense

Errors and ambiguity in visual perception

_______________ - Perception does not perfectly coincide with reality: it can mislead or fail us

• Autokinetic movement – you see movement where there isn’t any

• Agnosia (apperceptive and associative)

  • Prosopagnosia

Agnosia

Errors and ambiguity in visual perception

______________ - A failure or deficit in recognizing objects

• Not a result of dementia

• Can often recognize objects with other sensory modalities

• Prosopagnosia

• Apperceptive agnosia

• Associative agnosia

Prosopagnosia

_________________ - deficit in recognizing faces

• “The Man Who Mistook His Wife for a Hat”

Apperceptive agnosia

Errors and ambiguity in visual perception

________________ - deficit in recognizing pattern

Associative agnosia

Errors and ambiguity in visual perception

______________ - deficit in associating meaning and a pattern

Auditory sensory memory/echoic memory

Two types of sensory memory

_________________- A brief memory system that receives auditory stimuli and preserves them for some amount of time.

• Sound is a temporal event

Initial storage/duration

Echoic memory/auditory sensory memory

_____________ - Darwin, Turvey, and Crowder (1972) Simultaneous presentation of 3 lists of items through headphones at different spatial locations

• A light indicates which set to recall

• RESULTS:

  • Replicated Sperling's results

  • At short delays, partial>whole report

  • Max # of times recalled was 5 and echo lasted for 4 sec

  • Information was held in the echo much longer than it was held in the icon

Auditory persistence and erasure

Echoic memory/auditory sensory memory

______________ - Crowder & Morton (1969). Presented 9 digits visually (2 digits per second)

• 3 Conditions: Silent vocalization, active vocalization, passive vocalization

  • Silent: Reading silently, saying it in your head

  • Active: Read aloud, and name the numbers/letter

  • Passive: Read aloud by a recording

Results: For the last 3 items in the list, the active and passive vocalization groups made fewer errors

• Interpretation: active & passive groups could rely on echoic memory.

• Suffix Effect: inferior recall of the end of the list in the presence of an additional, meaningful, non-list auditory stimulus.

Auditory pattern recognition

Echoic memory/auditory sensory memory

• Templates: The problem of invariance: the sounds of speech are not invariant from one time to another

• Feature Detection: Bottom-up only, doesn’t account for top-down effects

• Conceptually Driven Processing

  • Pollack & Picket (1964): Presented words out of context

  • Two groups: one got recordings; one isolated word

Warren & Warren

Echoic memory/auditory sensory memory

______________ - participants are able to fill in gaps based on context.