Quiz 4 Sensory Psych

Inverse projection problem

Refers to the task of determining the object responsible for a particular image on the retina

Involves starting with the retinal image and then extending outward to the source of that image

(Why cant machines perceive like humans?)

Object can be hidden or blurred

People can often identify objects that are obscured and therefore incomplete, or in some cases objects that are blurry

(Why cant machines perceive like humans?)

Objects look different from different viewpoints

viewpoint invariance

(Why cant machines perceive like humans?)

Scenes contain high-level information

scenes are more complex

(why can't machines perceive like humans?)

Direct perception theories

- Bottom-up processing

- Perception comes from stimuli in the environment

- Parts are identified and put together, and then recognition occurs

Constructive perception theories

- Top-down processing

- People actively construct perceptions using information based on expectations

bottom-up processing

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information

perceptual organization

the process by which elements in the environment become perceptually grouped to create our perception of objects

good continuation

connected points resulting in straight or smooth curves belong together

lines are seen as following the smoothest path

(Principles of perceptual organization)

Pragnanz

every stimulus is seen as simply as possible

(Principles of perceptual organization)

similarity

similar things are grouped together

(Principles of perceptual organization)

proximity

things that are near to each other are groupged together

(Principles of perceptual organization)

common fate

thing moving in the same direction are grouped together

(Principles of perceptual organization)

common region

elements in the same region tend to be grouped together

(Principles of perceptual organization)

uniform connectedness

connected region of visual properties are perceived as single unit

(Principles of perceptual organization)

figure-ground segregation

determining what part of environment is the figure so that it "stands out" from the background

Properties of figure and ground

The figure is more "thinglike" and more memorable than ground.

The figure is seen in front of the ground.

The ground is more uniform and extends behind figure.

The contour separating figure from ground belongs to the figure (border ownership).

Factors that determine which area is figure

- elements located in the lower part of displays

- convex side of borders

subjective factors that determine which area is figure

Gestalt psychologists believed that experience and meaning play a role in minor perceptual organization

Gobson experiment showed that figure-ground can be affected by the meaningfulness of a stimuli

A scene contains:

-background elements

-objects organized in meaningful ways with each other and the background

Difference between objects and scenes

- A scene is acted within

- An object is acted upon

Research on perceiving gists of scenes

- Potter showed that people can do this

when a picture is only presented for 1/4

second

- Fei-Fei used masking to show that the

overall gist is perceived first, followed by

details.

Global image features of scenes

-degree of naturalness

-degree of openness

-degree of roughness

-degree of expansion

-color

(holistic and perceived rapidly)

physical regularities

regularly occurring physical properties

oblique effect (physical regularities)

people perceive horizontals and verticals more easily than other orientations

uniform connectedness (physical regularities)

objects are defined by areas of the same color or texture

(physical regularities) Homogenous color and nearby objects...

have different colors

Light-from-above heuristic (physical regularities)

light in natural environment comes from above us

semantic regularities

characteristics associated with the functions carried out in different types of scenes

palmer experiment

- Observers saw a context scene flashed

briefly, followed by a target picture. - Results showed that:

• Targets congruent with the context were identified 80% of the time .

• Targets that were incongruent were only identified 40% of the time.

Scene schema

knowledge of what a given scene typically contains

perception

determined by specific organizing principles, not just dark and light stimuli activating the retina

experience can influence perception but is not the key driver

perceiving and grouping for sound

location

proximity in time

good continuation

similarity

theory of unconscious inference

The idea proposed by Helmholtz that some of our perceptions are the result of unconscious assumptions that we make about the environment.

explains why stimuli can be interpreted in more than one way

likelihood principle

objects are perceived based on what is most likely to have caused the pattern

- created by helmholtz

Bayesian inference

idea that estimation of the probability of an outcome is determined by prior probability and likelihood of a given outcome

top-down processing

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

Grill-Spector experiment

examined the role of the FFA in face recognition using functional magnetic resonance imaging (fMRI) technology. participants briefly saw Harrison Ford's face followed by a mask, or a control stimulus followed by a mask (a). In (b), we can see the activity in the FFA when the participant recognized the photo as Harrison Ford and when the participant did not. Note that the highest response in the FFA is for correct recognition.

Experiment by Shienberg & logothetis

Monkey was trained to pull two levers: one for a sunburst and one for a butterfly

Binocular rivalry was used - each picture shown to one eye at the same time

Neuron in the IT cortex that responded only to the butterfly was monitored

Firing was vigorous for only the butterfly

Experiment by Tong et al

Binocular rivalry used again with people

Picture of a house shown to one eye and a face to another

Participants pushed button to indicate perception.

fMRI showed an increase in activity in

Parahippocampal place area for the house

Fusiform face area for the face

Experiment by Kamitani & Tong

Gratings with different orientations were presented to participants.

Responses from fMRI voxels were measured.

Activity patterns across voxels varies by grating orientation.

An orientation decoder was used to analyze the voxel activity.

The decoder could accurately predict which orientation had been presented.

Structural Encoding

relatively shallow processing that emphasizes the physical structure of the stimulus

bottom-up processing

Semantic encoding

the encoding of meaning, including the meaning of words

Top-down processing

Visual scanning

looking from place to place

fixation (visual scanning)

orientation of the eyes so that they image of a viewed object falls on each fovea

saccadic eye movement (visual scanning)

visual fixation jump from one location to another in the visual field

overt attention

involved looking directly at the attended object

covert attention

attention without looking

stimulus salience

areas of stimuli that attract attention due to their properties

-ex: color, contrast, movement, and orientation are relevant properties

attentional capture

involuntary shift of attention due to stimulus salience

saliency maps

show fixations are related to such properties in the initial scanning process

Experiment by Shinoda et al

- Observers' fixations were measured during

computer simulated driving.

- They were more likely to detect stop signs

when they were at intersections.

- People have learned that this is where stop

signs are typically placed.

task demands

-task demands override stimulus saliency

-eye movements and fixations are closely linked to the action the person is about to take

-Dynamic environments (where things are constantly changing)

-expectations of a dynamic environment change what we attend to

What happens when we attend?

Attention to specific locations is called spatial attention

1. attention enhances our response to objects

2. attention enhances our perception to objects

3. attention enhances our physiological response

Experiment by Posner (1978) et al.

How attention enhances our response

Observers looked at a fixation point.

Precueing with an arrow indicated on which side a stimulus was likely to appear.

Stimuli appeared that were consistent (valid trial) or inconsistent (invalid trial) with the cue.

Task was to push button when a target square was seen.

Results showed that observers responded fastest on valid trials

Posner believed these results showed that information processing is most efficient where attention is directed

Experiment by Egly et al.

- Observer views two rectangles.

- Cue signals where target may appear.

- Task was to press button when target

appeared.

- Results show:

• Fastest reaction time at targeted position

• "Enhancement" effect for non-target

within the target rectangle

Experiment by Carrasco et al.

Observers saw two grating stimuli with either similar or different contrast between the bars.

Task was to fixate on center point between gratings and indicate orientation of bars with higher contrast.

Small dot was flashed very quickly on one side before gratings appeared.

Results showed that:

When there was a large difference in contrast, the dot had no effect

When contrast was the same, observers were more likely to report that grating preceded by the dot had higher contrast

This the shift of attention led to an effect on perception

O'Craven (1999)

subject attended to the house or face show that attending to the moving or stationary face caused enhanced activity in the FFA and attending to the moving or stationary house caused enhanced activity in the PPA

fMRI study

Participants used covert attention to focus on different areas

Attention to locations increases the response at specific areas in the brain

Datta and DeYoe (2009)

Attention maps show directing attention to a specific area of space activates a specific area of the brain.

Womelsdorf (2006)

Showed that attention can cause a monkey's receptive field to shift toward the place where the attention is directed

What happens when we don't attend?

inattentional blindness and change blindness

inattentional blindness

a stimulus is not perceived even when the person is looking directly at it

change blindness

Observers were shown a picture with and without a missing element in an alternating fashion with a blank screen

Results showed that the pictures had to alternate a number of times before the change was detected

When a cue is added to show where to attend, observers noticed change more quickly

Experiment by Simons and Charbis (1999)

Observers are shown short film teams passing a basketball

Task is to count number of passes

Either a woman with an umbrella or a person in a gorilla suit walks through the teams

46% of observers fail to report the woman or gorilla