Sensation is the activation of one or more of the senses by something in our environment. Perception is the selection, organization, and interpretation of sensory input. Sensation involves the stimulation of sensory organs, whereas perception involves the interpretation of sensory input. These two processes merge at the point where sensory receptors convert physical energy into neural impulses.

All of our senses receive sensory stimulation, transform that information into neural impulses, and deliver information to the brain. The process of converting one form of energy to another (or, in this case, converting sensory stimulation into neural signals) is called transduction. The field of psychophysics studies the relationships between the physical characteristics of stimuli and our psychological experience of them.

• Top-Down Processing: information processing guided by “higher level” mental processes, i.e. perception first

  • Perceptual set: a mental predisposition; the experiences, assumptions, and expectations that influence our perception

• Bottom-Up Processing: begins with sense receptors and works up to the brain, i.e. sensation first

The absolute threshold for a specific type of sensory input is the minimum stimulus intensity that an organism can detect 50% of the time. Thresholds can be thought of as boundaries or limits to our senses. 

• Examples:

  • Vision: a candle flame seen at 30 miles on a dark night

  • Hearing: the tick of a watch under quiet conditions at 20 feet

Gustav Fechner, a scientist pre-dating Wundt, was interested in people’s sensitivity to differences between stimuli. The just noticeable difference is the smallest difference in a stimulus intensity that specific sense can detect. Difference threshold: the minimum difference between two stimuli required for detection 50% of the time

• Examples: recipes, showers, dimmers, radio volume, etc. 

• Weber’s Law: the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage, rather than a constant amount

Signal detection theory proposes that the detection of stimuli involves decision processes as well as sensory processes, both of which are influenced by a variety of factors besides stimulus intensity (i.e. being able to pick out a specific stimuli while receiving multiple stimuli).

Selective attention is our inability to consciously perceive all the sensory information available to us at any point in time.

• Change blindness is lack of awareness of minute changes made in our environment.

• Another example of selective attention can be seen in the cocktail party effect or phenomenon. The cocktail-party effect refers to the ability to focus one's attention a particular stimulus while filtering out a range of other stimuli (i.e., noise). For example, you’re in a crowded room in the middle of a conversation with someone else. You can focus on the conversation you’re having and ignore those going on around you.

Sensory adaptation is a gradual decline in sensitivity to prolonged stimulation. Automatic process which allows organisms to ignore the obvious and adjust to changes quickly. When you know the water is cold, you are hesitant to jump in, but all the adults say the same thing - “you’ll get used to it after a few minutes”. You jump in, are frozen for a moment, and then start to acclimate to the water. Up until now, you have ignored much of the information from your senses because they’ve been exposed to constants, but now that I’m bringing it to your attention (the smell of the room or your perfume, the feeling of the clothes on your skin), you notice it again.

Subliminal perception is the registration of sensory input without conscious awareness.

• • Consumer behavior – using subliminal messages to sell everything from weight loss drugs to music

Parallel Processing: processing multiple aspects of a sense at once; for vision, this includes color, motion, form, and depth. 

Priming is a phenomenon in which exposure to one stimulus influences how a person responds to a subsequent, related stimulus. Through experience, we come to expect certain results. Those expectations may give us a perceptual set - a mental predisposition to perceive one thing and not another.

Light travels in waves, and the shape of those waves influences what we see. Light’s wavelength (distance from the peak of one wave to the next) determines the hue (color). The wave’s amplitude (height) determines the intensity (the amount of energy the wave contains) or brightness. The purity of the wave determines how vivid the color appears. 

Light enters the cornea (the eye’s clear, protective layer) and then the pupil (adjustable opening of the eye allowing light to pass through) whose size is determined by the iris (colored ring of muscle tissue). Light is then focused by the lens (transparent structure which changes shape to focus images) on the retina (the light sensitive inner surface of the eye with layers of neurons to convert light into neural impulses). The process of focusing these images is called accommodation. These neural impulses are carried to the brain via the optic nerve.

• Cornea – protective covering of the eye; transparent, allowing light to pass through

• Lens – focuses the light rays on the retina

• Retina – transduction organ of the eye; absorbs light, processes images, and sends visual information

• Iris – colored muscle that controls the size of the pupil and regulates the amount of light entering the eye

• Pupil – allows light to pass into the rear chamber of the eye

• Cones: specialized visual receptors that play a key role in daylight vision and color vision

• Rods: specialized visual receptors that play a key role in night vision and peripheral vision

• Fovea: “focal point”, contains only cones and the point at which visual acuity is at its greatest

• Optic Disk: “blind spot”, a hole in the retina where the optic nerve fibers exit the eye

Retinal disparity refers to the fact that objects within 25 feet project images to slightly different locations on the right and left retinas, so each eye has a slightly different view of the object. As the object gets closer, the greater the disparity seen by each eye. 

Accommodation: The process by which the eye’s lens changes shape to focus on near or far objects on the retina. 

Eleanor Gibson & the Visual Cliff Experiment: As the infants were able to detect the danger from the 'cliff' side, Gibson concluded that their depth perception is learned as soon as they could crawl. 

Feature detectors are nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. For humans, we have specialized feature detectors for faces. Damage to these feature detectors or the area of the temporal lobe responsible for facial recognition could lead to prosopagnosia (also known as face blindness or facial agnosia)- a neurological disorder characterized by the inability to recognize faces.

Figure-ground is the organization of the visual field into objects (figures) that stand out from their surroundings (the background). 

A visual illusion involves an apparently inexplicable discrepancy between the appearance of a visual stimulus and its physical reality. Note: The picture on the left is not a gif, but it looks like it's pulsing. 

Common illusions:

• Müller-Lyer: illusion of line length that is distorted by inward-turning or outward-turning corners on the ends of the lines, causing lines of equal length to appear to be different.

• Ames Room: Due to the shape of the room-trapezoid, the person standing to the right side of the room appears much larger.

• Moon Illusion: moon always appears larger on the horizon than it does overhead

• Ponzo Illusion: an optical illusion in which two identical figures are made to appear of different sizes because of the effect of perspective

Perceptual constancy is the ability to perceive objects as unchanging even as illumination and retinal images change. For example, when you look out the window of a plane, you know that you aren’t seeing tiny cars on tiny highways, but rather that the cars are normal size and just very far away. Regardless of our view of them, objects maintain the same:

• • Shape Constancy

  • Size Constancy

  • Color Constancy

  • Brightness Constancy

    • However, color and brightness also depend on context!

Audition is our sense of hearing. Like light, sound travels in waves. Sound waves are composed of compression and rarefaction of air molecules. The height of the wave, or amplitude, determines the volume of the sound, measured in decibels. The frequency (number of wavelengths that pass a point in a given time) determines the pitch (highness or lowness of tone). 

Sound waves are funneled into the auditory canal by the pinna (exterior part of ear). Once in the ear canal, sound waves vibrate the eardrum (tight membrane preceding the middle ear), then the hammer/malleus, anvil/incus, and stirrup/stapes (also known as the ossicles), finally vibrating the oval window of the cochlea (the coiled, bony, fluid-filled tube of the inner ear responsible for transduction of sound). The cochlea is lined with a basilar membrane (a layer of hair cells which convert the sound waves into neural impulses). Neural impulses are carried to the brain via the auditory nerve.

• Pinna: external visible portion of ear; funnels sound waves into the ear canal

• Eardrum: taut membrane that vibrates in response to sound waves

• Ossicles: (hammer, anvil, stirrup or malleus, incus, stapes) amplify changes in pressure and transmit vibrations received by eardrum

• Cochlea: transduction organ of the ear; contains basilar membrane with hair cells which convert sound waves into neural signals

The volley principle states that groups of neurons of the auditory system respond to a sound by firing action potentials slightly out of phase with one another so that when combined, a greater frequency of sound can be encoded and sent to the brain to be analyzed.

Think of a twenty-one gun salute. You don't hear each individual shot, but just one single boom. Without the volley principle, all sounds you heard would be muddied like that.

Olfaction, or our sense of smell, is also a chemical sense and works closely with taste through a process called sensory interaction (when one sense influences another). This is why if you plug your nose or have a bad sinus infection and can’t smell, you also lose your sense of taste.

Odorants enter the nasal cavity to stimulate 5 million receptors in the olfactory bulb to sense smell, and then it bypasses the thalamus and goes straight to the temporal lobe to be processed. Scientists suspect this is an evolutionary trait, as smell is our first indication that food has spoiled and will likely make us ill if consumed. This could also explain why smell is closely connected to memory; if something made us ill in the past, its smell will be a reminder not to eat it again (taste aversion). 

Gustation, or our sense of taste, is a chemical sense. The small bumps on the surface of the tongue are called papillae. They serve as our taste receptors. There are five identified taste sensations:

• Sweet - helps us identify sugary foods for energy

• Sour - helps us identify foods that have gone bad or could make us sick

• Salty - sodium is essential for physiological functioning

• Bitter - helps us identify poison or foods that could make us sick

• Umami (savory) - helps us identify foods high in protein which help grow/repair tissue

Touch, our tactile sense, is vital to our development and survival. Contact comfort helps us establish bonds with caregivers, and premature babies have a better chance of survival if they are held. The touch sensations include pain, pressure, and temperature, and are processed by our parietal lobe. Perception is inherently subjective, particularly pain.

Pain tells the body that something has gone wrong, usually resulting from damage to the skin and other tissues. Pain begins at sensory neurons known as nociceptors. 

Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed. Gate-control theory states that the spinal cord acts as a buffer between pain and the brain, deciding which signals will pass through; pain is a function of the balance between the information traveling into the spinal cord through large nerve fibers and information traveling into the spinal cord through small nerve fibers.

“Gate-Control Theory” of Pain

• spinal cord blocks or allows pains signals to pass to brain

• small nerve fibers “open” the gate

• large nerve fibers “close” the gate

Pain is not merely a physical phenomenon of injured nerves sending impulses to a definable brain or spinal cord area. The brain can also create pain, as it does in phantom limb sensations after a limb amputation. Without normal sensory input, the brain may misinterpret and amplify spontaneous but irrelevant central nervous system activity. As the dreamer may see with eyes closed, so 7 in 10 such people feel pain or movement in nonexistent limbs. As we learned last unit, endorphins serve as natural painkillers, thus preventing pain signals from going to the brain. 

The sense of our individual body parts’ position and movement is called kinesthetic sense. 

• Receptors in the muscle tissues and joints

The vestibular sense monitors the head and body position, as well as, our sense of balance.

• Receptors in the semicircular canals and vestibular sacs of the ear

• Works with cerebellum

Extrasensory Perception (ESP) - claim of perception that occurs without the use of normal sensory channels such as sight, hearing, touch, taste, or smell.

• Telepathy -ability to read another person’s thoughts, or mind reading.

• Clairvoyance - ability to “see” things that are not actually present. 

• Precognition -  ability to know something in advance of its occurrence or to predict a future event. 

Parapsychology - the study of ESP, ghosts, and other subjects that do not normally fall into the realm of ordinary psychology.