Sensation and Perception

What are Sensation and Perception? Sensation is the information we receive from our five senses (sight, taste, touch, smell, and hearing) The information goes to the CNS, where the brain interprets it Perception is our interpretation of that information and how we react to it We perceive information based on learning, past experiences, and attitudes

Absolute Thresholds An absolute threshold is the weakest amount of a stimulus that can be sensed Scientists have determined absolute thresholds for all five senses for the average person, but they vary by individual Absolute thresholds for humans are different than those for animals (a dog’s hearing threshold is very different from ours

Difference Thresholds A difference threshold is the minimum amount of difference we can detect between two stimuli Think of hearing the notes of different keys on a piano These differ from person to person as well

Signal Detection Theory Many internal and external forces affect our ability to detect sensory information SDT is the method of taking into account the strength of a stimulus but also environmental influences and an individual’s physical state and attitudes It is much harder to detect the sound of someone’s voice in a quiet room than it is in a noisy one The buzzing of fluorescent lights may be more distracting when you are stressed or have a headache People tend to focus more on what they personally find important and ignore what they find unimportant

Sensory Adaptation The process by which we become more sensitive to weak stimuli and less sensitive to unchanging stimuli When you enter a very dark room, your eyes adapt to the new space and begin to detect weak sources of light If you live in the city, your ears adapt to the constant sound of traffic in the background and detect other noise sources

Vision

Light Light is electromagnetic energy measured in wavelengths Not all light is visible to humans Visible light can be filtered into a variety of colors – each color has a different wavelength Blue and violet have the shortest wavelengths, red has the longest

The Eye Works similar to a camera Light enters the eye through the pupil The lens adjusts to the distance of objects by changing its thickness The image then is projected onto the retina – it acts like film in a camera Neurons on the retina, called photoreceptors, react to the light and send the image to the occipital lobe of the brain

Rods, Cones, and the Blind Spot Rods and cones are types photoreceptors that cover the retina Rods – only sensitive to brightness of light, allow us to see in black and white Cones detect colors within the light The blind spot is the area of the eye that connects to the optic nerve – it does not have rods or cones and does not capture a light image at all

Color and Vision People with normal vision can see any color in the visible light spectrum, but not all animals can Cones in the eye are sensitive to certain colors – either blue, green, or red When more than one type of cone is stimulated, we can perceive other colors like yellow, orange, and purple TVs and computer screens use only blue, green, and red pixels to create color images

Color Blindness People may be partially color blind if they cannot see all of the colors in the color spectrum This occurs when cones malfunction or when people are born without a certain type of cone Total color blindness occurs when people cannot see any colors, only black and white – this is a really rare condition

Hearing

Sound and Pitch Sound is caused by vibrations that travel through the air in waves How fast they complete a cycle determines their pitch Shorter waves produce a higher pitch Longer waves produce a lower pitch A violin produces a higher pitch than a cello, which has longer strings and makes longer sound waves

Loudness Loudness is measured by the height of sound waves – this is known as amplitude and is measured decibels The absolute threshold of sound for humans (0 decibels) is the sound of a ticking watch 20 feet from the ear in a quiet room

The Ear Shaped to capture sounds, vibrate with them, and transmit the sound to the brain The eardrum is the thin membrane gateway between the outer and inner ear As sound hits the eardrum, it vibrates and transmits the sound to three small bones These bones vibrate the cochlea, a small bony tube filled with fluid and neurons that react to movement and send messages to the auditory nerve The auditory nerve sends messages to the temporal lobe

Deafness Conductive deafness – caused by damage to the middle ear, which amplifies sounds – can be treated with a hearing aid that amplifies noises Sensorineural deafness – caused by damage to the inner ear or destruction of neurons in the cochlea, usually from prolonged exposure to loud noises – can be treated (sometimes) with cochlear implants

Smell, Taste, and Touch

Smell Smell is linked with taste – when your ability to smell is impaired, your ability to taste decreases Molecules in odors travel into the nose and contact receptor neurons high in the nose These neurons send messages to the olfactory nerve Our sense of smell is highly adaptable and we can quickly lose our awareness of certain smells

Our sense of taste is connected to smell, texture, and temperature Apples and onions taste very similar, but their odors create very different flavors We can distinguish four main taste qualities – sweet, sour, bitter, and salty Receptor neurons on the tongue detect various qualities and send information to the brain We regularly kill taste receptors, but they grow back within a week – the taste system is the most resilient of our senses Taste

Skin Senses Our skin can detect pain, pressure, and temperature – some receptors detect just one type of stimulus while others may detect all three Many receptors are located at the roots of our body hair They are not evenly distributed – parts of the body have many more receptors than others

Temperature and Pain Receptors Temperature receptors are just below the skin, some detect warmth while others detect cold Our sense of temperature is adaptable, we acclimate to warmer or cooler settings pretty quickly Pain receptors motivate the body to try and stop the painful stimulus Sometimes we can overload the brain’s messages to ease pain – rubbing an injury can distract the brain from pain signals

Body Senses Vestibular Sense – our sense of balance – tells us when we are upright and whether we are falling or changing speed Allows us to know that we are standing up or moving in an elevator when our eyes are closed Kinesthesis – the sense that informs people about the position and motion of their bodies Allows us to touch our nose with our eyes closed

Perception

How Do We Organize Sensory Information? Our brain learns to use a variety of methods to sort and make sense out of sensory information Closure Figure-ground perception Proximity Similarity Continuity Common fate

Closure The tendency to perceive or complete a whole figure even when there are gaps in what your senses tell you You try to fit the pieces you have into a familiar pattern to create a whole image

Figure-Ground Perception The perception of figures against a background our perception can change depending on what we interpret as a background and what we view as a figure We use this method of perception every day

Proximity Grouping objects because of its nearness to other objects there is no reason to group the objects other than the fact it is located next to other objects

Similarity The process of grouping similar objects together People often perceive of similar objects as being a part of the same group, even if they could be grouped differently

Continuity People prefer to see smooth, continuous patters rather than disrupted ones

Common Fate People or objects that move together or perform the same action must have the same purpose A group of people running in the same direction must all be running to the same place – they have a common fate

Perception of Movement We perceive movement when we see an object move in relation to other objects We look for stable objects to use as markers for movement (buildings, trees, the sidewalk)

Stroboscopic Motion An illusion of movement Created by showing a rapid series of images or objects that are not moving, but each image is just slightly different than the previous one (flip books) Movies work in a similar way

Depth Perception People use two main cues to gauge distances Monocular cues – need only one eye to be perceived Perspective, clearness, overlapping, shadowing are used to determine which objects are closer and which are farther away Binocular cues – need two eyes to be perceived Retinal disparity – each retina captures different images of an object (finger test) Convergence – our eyes try to maintain a single image of an object and turn inward, or converge, as the object gets closer

Constancies Everybody creates constancies in their minds They are based on size, color, brightness and shape

Size Constancy We perceive of an object to be one size no matter how far away it is and even though is creates a different-sized image on the retina We base size constancy on past experiences We know that a dog standing 20 feet away is the same size as if it was right next to us, even though our eye senses a smaller image

Color Constancy We know that certain objects do not change colors even though we may not be able to see the colors I know my house is the same color in the nighttime that it is during the day even though I cannot see its color without light

Brightness Constancy We perceive of an object as being equally bright even when the intensity of light around it changes

Shape Constancy We know that an object does not change shape even though it may look different from various angles We know that a door is rectangular even though it may look like a trapezoid from some angles

Visual Illusions Sometimes our constancies cause us to interpret information incorrectly The visual cues we use fool our brains into perceiving objects as having a different size, shape, or color than they actually do