chapter 5 sensation/perception

1. Inverse Projection Problem

The image on your retina is 2D, but the brain has to determine what 3D object in the real world created that image.

Many different objects can create the same retinal image, so the brain has to interpret which object is actually there.

Example: A small object nearby and a large object far away could create the same-sized image on your retina.

Occlusion

When one object blocks part of another object, but we still perceive the hidden object as whole and continuous.

If a person is standing behind a tree and you only see their head and legs, you don't think you're seeing separate body parts. Your brain assumes one complete person continues behind the tree.

Viewpoint Invariance

The ability to recognize an object from different viewing angles.

The image an object creates on your retina changes when your viewpoint changes, but you still need to recognize it as the same object.

You can recognize a chair from the front, side, or at an angle even though each view creates a different retinal image.

Perceptual Organization: Grouping vs. Segregation

how the brain organizes pieces of visual information into meaningful objects.

Grouping = putting things TOGETHER
Your brain decides which visual elements belong to the same object or group.

Example: If you see dots that are close together, you tend to perceive the nearby dots as belonging together.

Segregation = separating things APART
Your brain determines which areas belong to different objects, especially separating the figure from the background (ground).

Example: A black shape on a white page → your brain decides the black shape is the figure and the white area is the background/ground.

What is the Gestalt approach?

says that we perceive whole, organized objects, rather than simply adding up individual sensations or features.

Main idea: “The whole is different from the sum of its parts.”

When you look at a face, you perceive a whole face, not separate eyes + nose + mouth that your brain then adds together.

How did Gestalt differ from Structuralism?

Structuralism:

• Tried to break perception down into its smallest individual components/sensations.

• Perception = combination of these individual pieces.

Gestalt:

• Said perception cannot be fully understood by breaking it into pieces.

• The brain naturally organizes information into meaningful wholes.

🧩 Structuralism = pieces
🖼 Gestalt = whole picture

Apparent Movement

perceiving movement even though nothing is actually moving.

It occurs when stationary stimuli are presented rapidly in slightly different locations, causing your brain to perceive continuous motion.

Example: Two lights flash quickly in different locations:

Light 1 💡 → Light 2 💡

Neither light moves, but you perceive one light moving from one location to the other.

why does apparent movement give evidence for gestalt

Because none of the individual stimuli actually contain movement, yet when they are presented together in the right sequence, your brain creates the whole experience of motion.

perception cannot be explained only by adding up individual sensations

Proximity

Things that are close together are perceived as belonging together.

Example:
● ● ● ●
You see two groups of dots because the dots within each pair are closer together.

Proximity = close = grouped

Similarity

Things that look similar are perceived as belonging together.

Example:
● ● ▲ ▲ ● ●
You tend to group the circles together and the triangles together.

Similarity can involve shape, color, size, orientation, etc.

Similar = same group

Good Continuation

We tend to perceive lines as following the smoothest, most continuous path, rather than suddenly changing direction.

If two lines cross like an X, you perceive two continuous lines crossing, rather than four separate lines meeting in the middle.

Good continuation = keep the line going smoothly

Connectedness

Things that are physically connected are perceived as belonging together.

Example:

●—● ●—●

You perceive each pair connected by a line as one group.

Memory: Connected = grouped

Common Fate

Things that move in the same direction are perceived as belonging together.

Example: A group of birds flying in the same direction is perceived as one flock.

🐦→ 🐦→ 🐦→

Memory: Moving together = grouped together

Common Region

Things located within the same enclosed area are perceived as belonging together.

Example:

[ ● ● ] [ ● ● ]

Even if all four dots look identical, the dots inside each box are perceived as separate groups.

Memory: Same area = same group

Pragnanz / Good Figure / Simplicity

We tend to organize visual information in the simplest, most stable way possible.

Example: If a circle overlaps a square, you usually perceive a complete circle and a complete square overlapping, rather than several complicated, oddly shaped pieces

Pragnanz = brain prefers SIMPLE

What is Figure-Ground Segregation?

Figure-ground segregation = the process of separating an object (the figure) from its background (the ground).

• Figure = the object you are focusing on

idea more thinkable or more memorable

• Ground = the background behind the object

unformed material without specific shape

(edge seemed to correlate with the figure)

• 
  

perceptual segregation

the brain is deciding what should be perceived as a separate object.

process in which elements grouped to created perception objects

What determines which area becomes the figure?

Lower region- areas lower In visual field derived as the figure

ex-idea that buildings in a skyline picture even if black and white seen to be figure and background is behind it

convexity- areas on the convex side of a border more likely perceived as figure

-convex side is the side of a border that bulges outward or curves outward, like the outside of a circle.

past experience with familiarity and regonitiztion can influence

important: gestalt originally thought past experiences did not influence perceptual organization (thought to be innate)

figure vs ground easy

figure

-object in front, owns border, and more memorable

gound

-background behind figure continuous

Physical Regularities

are characteristics of the environment that occur frequently, which the brain learns and uses to help interpret what we see.

Vertical and horizontal orientations occur frequently in our environment, so our visual system is particularly sensitive to them.

what are 3 physical regularities

-oblique effect

-light-from-above

-semantic regularities

Oblique Effect

he oblique effect is that we perceive horizontal and vertical orientations more accurately than diagonal (oblique) orientations.

bc more neurons detect these lines

You would generally be better at detecting whether a vertical | line is slightly tilted than detecting the same change in a diagonal / line.

Light-From-Above Assumption

The light-from-above assumption is our tendency to assume that light normally comes from above when interpreting objects and shadows.

If part of a circle is lighter at the top and darker at the bottom, your brain may interpret it as a 3D object that bulges outward, because it assumes the light source is above it. (think of sandy feet examples and how when you flip the opposite ways due to shadowing the initial indent looks like a bulge

Semantic Regularities

are our knowledge about what objects are typically found in certain environments or scenes.

what belongs where based on previous experience.

In a kitchen, you expect to see:

• Stove

• Refrigerator

• Sink

• Plates

NOT A TOLIET

-help us quickly perceive objects within scene

(given list of objects expect to see bread instead of mailbox in kitchen)

-influence recognition -saying what blob was with top down processing or knowledge of scene based on context

what is an additional part of semantic regularity

scene schema

is our knowledge about what is typically contained in a particular scene or environment.scene schemas

It is a type of semantic regularity because it comes from our knowledge and past experience about what belongs where.

quickly understand scenes and recognize obj

Greeble study method

grebes: unfamiliar, complex objects designed to share some face-like properties, with different individual Greebles having similar overall structures.

Definition: Researchers compared people's FFA (fusiform face area) activation for faces versus Greebles, both before and after people were trained to recognize Greebles.

what occurred

• Before training: Participants were unfamiliar with Greebles.

• Participants then received Greeble recognition training, becoming much better at distinguishing individual Greebles.

• After training: Researchers measured FFA responses again.

It's like becoming an expert at telling apart many objects that initially all look very similar.

Before training:
👉 Faces produced much greater FFA activation than Greebles.

After Greeble recognition training:
👉 Faces and Greebles produced more similar FFA activation.

Implications (possible effect)

: The results questioned the idea that the FFA is only a specialized face-processing module.

the idea that faces wee only recognized with ffa

instead

The FFA can respond to complex objects other than faces, especially objects for which someone has developed expertise.

So experience can actually influence how strongly the FFA responds to certain object

Expertise Hypothesis

he expertise hypothesis proposes that the FFA is involved in recognizing and distinguishing objects for which a person has developed high levels of perceptual expertise, rather than being exclusively dedicated to faces.

idea faces are an object expertise due to the frequencies of exposure and different identities to them