Perception How your mind understands sensory information

Sensation vs. Perception Sensation – to construct the outside world inside our heads we must detect physical energy from the environment and then encode it as neural signals. –Bottom-up processing—Data-driven where sensory information travels from receptors to the brain. –assembling a jig-saw puzzle without the picture Perception - The process of integrating, organizing, and interpreting sensory information –Top-down processing— Draw upon our knowledge, experiences & expectations to arrive at meaning. Also called conceptually driven processing. –using the picture to assemble the jig-saw puzzle Sensation and Perception blend into one continuous process, progressing upward from specialized detector cells and downward from our assumptions.

Selective Attention At any moment we focus our awareness on only a limited aspect of all that we are capable of experiencing. Cocktail party effect – the ability to attend selectively to only one voice among many. True for visual attentiveness – Neisser study with woman & umbrella - Examples of Change Blindness. True for auditory attentiveness – Wilson experiment where person listens to two separate conversations (one in each ear). Can only listen to one at a time. Unattended stimuli can have subtle effects. If someone says your name at a party, your perceptual system may bring that voice to consciousness. We are constantly filtering sensory info and inferring perceptions in ways that make sense to us. Look at Necker Cube on oncoming slide – because attention is selective, you can see only one interpretation at a time.

Gestalt Founded by Max Wertheimer, it emphasizes that we view things as a unified whole or figure rather than in isolated bits and pieces Given a cluster of sensations, the human mind organizes them into a Gestalt Gestalt psychologists stressed that the whole is greater than the sum of its parts. By breaking experiences into their basic parts, something important is lost.

A Gestalt Figure & Selective Attention What do you see: circles with white lines, or a cube? If you stare at the cube, you may notice that it reverses location, moving the tiny X in the center from the front edge to the back. At times the cube may seem to float in front of the page, with circles behind it; other times the circles may become holes in the page through which the cube appears, as though it were floating behind the page. Because attention is selective, you see only one interpretation at a time. For an online demo click below: Necker CubeNecker Cube

Temple or Tunnel?

To transform sensory information into meaningful perceptions our perceptual processes help us organize info so we can answer 3 questions: 1. What is it? 2. How far away is it? 3. Where is it going? Organizational Principles

What is It? Perception of Shape We primarily rely on shape to identify things in our environment. Dax Experiment showed this in 3-year-olds. As long as the object had the same shape as the original dax, the children identified it as a dax.

How Far Away Is It? Figure-Ground Relationships

Figure and Ground Gestalt Psychologists also thought that an important part of our perception was the organization of a scene in to its: Figure—the object of interest Ground —the background Pictures have reversible figure-ground Different neurons in the brain fire for shapes that are figure than do for shapes that are ground.

Another Figure-Ground Example Do you see musicians or old people?

M.C. Escher

What’s the figure in this picture? Having trouble? Click HERE or HEREHERE

Illusions An object’s background can change and make us perceive things that are not really present. Click on the video clip below. Are the lines slanted or straight? The Café Wall Illusion

Zollner Effect Are these squares straight? Straight lines appear to bend if they intersect with or are seen against a background of curved lines. Your eyes and brain are working together to try to make the straight lines fit the background pattern.

Spiral Square Case Are these squares bent? The curves of the spiral in the background make the square seem bent. Ground has a role in how we perceive the figure.

Are the letters tilted? “Now, squint your eyes to see it straight” - Laura Kooistra

Organizational Principles: Grouping Principles

Law of Pragnanz (Simplicity) When several perceptual organizations are possible, the simplest and most stable shape will be perceived What do you see? You probably perceived this image as that of three overlapping squares rather than as two six- sided objects and one four-sided object.

Grouping Organizing the figure information into meaningful forms. The perceptual tendency to organize stimuli into understandable groups Several principles of grouping include: –Similarity –Proximity –Closure –Continuity ( Good Continuation)

Grouping - Similarity The tendency to place items that look similar into a group

We perceive objects of similar size, shape, or color as a unit or a figure

Grouping - Proximity The tendency to place objects that are physically close to each other in a group

Our tendency perceive objects that are close to one another as a unit or a figure. We see three sets of two line or two groups of three people.

Grouping – Closure The tendency to look at the whole by filling in gaps in a perceptual field

Our tendency to fill in the gaps or contours in an incomplete image. Completing or Connecting the object

Grouping – Continuity We perceive lines as smooth continuous patterns rather than discontinuous ones. Once an object appears to move in a particular direction, your brain assumes that the movement continues unchanged. Also known as Law of Good Continuation

Our tendency to group lines that appear to follow in the same direction as a single unit or figure. Seeing the line as continuous and the curves as continuous.

Connectedness When they are uniformed and linked, we perceive spots, lines, or areas as a single unit.

These Grouping Principles Can Lead us Astray… You probably perceive this doghouse as a gestalt—a whole (though impossible) structure. Actually, your brain imposes this sense of wholeness on the picture. As the photo on page 225 shows, gestalt grouping principles such as closure and continuity are at work here.

Impossible Figures Revealed It’s a matter of perspective!