Sensation & Perception

How we perceive the world is much more than just an image transmitted to our brains!

• Sensation- The process by which our sensory receptors & nervous system receive & represent stimulus energies from our environment.

• Perception- The process of organizing & interpreting sensory information, enabling us to recognize meaningful objects and events.

How does our brain make sense of what we perceive?

• Bottom-up processing- Analysis that begins with the sensory receptors & works up to the brain’s integration of sensory information

• Top-down processing- Information processing guided by higher level mental processes, as when we construct perceptions drawing on our experience & expectations

Light & Color

Wavelength- the distance from the peak of one light or sound wave to the peak of the next.

Intensity- the amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by the wave’s amplitude

What is color?

A strawberry isn’t actually “red”. In fact, it doesn’t contain any qualityof “redness”.The strawberry actually absorbs all light except red which is reflected back to our eyes.After that, our brain interprets this wavelength as “red”

How do we “see”?• Seeing is a process that involves the human

eye, the thalamus, the occipital lobe and various other parts of the brain.

Outer Eye Structure

Outer eye structure

• Pupil- The adjustable opening in the center of the eye through which light enters. Operates like the aperture of a camera.

Outer eye structure

• Iris- a ring of muscle tissue that forms the colored portion of the eye around the pupil. Controls the size of the pupil opening

Outer eye structure

• Lens- the transparent structure behind the pupil that changes shape to help focus images on the retina.

Inner Eye Structure

Inner Eye Structure

• Retina- the light sensitive inner surface of the eye, containing rods & cones plus layers of neurons

Rods and Cones!!• Rods- retinal receptors that detect black,

white, & gray. Primarily used for peripheral & twilight vision.

Rods and Cones!!

• Cones- retinal receptors that are concentrated near the center of the retina & function in daylight or well-lit conditions.

Cones also detect fine detail and colors

Inner Eye Structure

• Optic nerve- the nerve that carries neural impulses from the eye to the brain

Inner Eye Structure

• Fovea- the central focal point in the retina, around which the eye’s cones cluster.

Inner Eye Structure

• Blind spot- the point at which the optic nerve leaves the eye. This creates a “blind spot” because no receptor cells are located there

Blind Spot

Young-Helmholtz Trichomatic theory

• The theory that the retina contains three different receptors.

One most sensitive to redOne most sensitive to blueOne most sensitive to green

• When stimulated in combination, they can produce the perception of any color

ThresholdsAbsolute threshold- the minimum stimulation needed to detect a particular stimulus 50% of the time.

Hearing Test!

Signal Detection Theory

A theory predicting how and when we detect the presence of a faint stimulus or signal and background stimulation (noise).This theory assumes that there is no single absolute threshold & that detection depends on a person’s experience, expectations, motivation, and alertness.

Signal Detection Theory

What might affect our ability to detect signals properly?

Priming- the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.

Talking Dogs!

More on priming….

Backwards Lyrics

Perceptual SetA mental predisposition to perceive one thing and not another.

Let’s take a quick test……..

Write down what you see….

Write down what you see

Write down what you see

Write down what you see

Difference Threshold

The minimum difference between two stimuli required for detection 50% of the time. We experience the difference threshold as a “just noticeable difference”

Thresholds

Subliminal messages…..

Subliminal- below one’s absolute threshold for conscious awareness at least 50% of the time.

Weber’s Law

The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage.

Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.