Other senses & perception 4.4 & 4.5

Other senses We perceive smell and taste by sensing the molecules of certain substances. Sensory receptors on our skin allow us to sense pressure, temperature, and pain. Body senses help us keep our balance and stand up straight.

Smell Smell and taste are called the chemical senses. Unlike vision and hearing, which uses physical energy to stimulate sensory receptors, with smell and taste, we sense molecules of substances. Smell is the sense that helps recall the most memories. People do not have as strong a sense of smell as many animals do. Odors are detected by receptor neurons in the nose. The receptors send information about the odors to the brain via the olfactory nerve. Our sense of smell adapts quickly. (locker rooms) Some people also lose awareness of some smells. (smokers)

taste Most researchers agree on four basic taste qualities: sweet, sour, salty, and bitter. Some researchers argue that there is a savory basic taste called umami, which means “meaty” or “savory” We sense taste through receptor neurons located on taste buds on the tongue. Flavor depends on odor, texture, and temperature as well as taste. If it were not for odor, heated tenderized shoe leather might pass for a steak. Taste cells reproduce rapidly. People who claim to enjoy very bitter foods may actually be “taste blind” to them. Dogs can taste sweetness, but cats lack that ability.

Skin senses Touch is called the skin senses because it is a combination of pressure, temperature, and pain. Our skin senses are vitally important to us. Premature infants grow more quickly if they are touched, and petting an animal can actually lower a person’s blood pressure.

Skin senses Pressure temperature Sensory receptors located around the roots of hair cells fire where the skin is touched. The fingertips, lips, nose, and cheeks are more sensitive than the shoulders, thighs, and calves. The receptors for temperature are neurons just beneath the skin, causing receptors to fire for both warmth and cold. When you go outside on a hot day, or when you jump into a cold pool, you adapt to temperature changes.

pain The more pain receptors located in a particular area of our skin, the more sensitive that area is. Chemicals called prostaglandins help the body transmit pain messages to the brain. Gate theory suggests that only a certain amount of information can be processed by the nervous system at a time, like too many calls are flooding a switchboard.

Body senses kinesthesis Vestibular sense Kinesthesis is the sense that informs people about the position and motion of their bodies. This is why when you close your eyes, you can still find your nose. How can you locate your nose if you can’t see your hands? You can also navigate your way through a room without bumping into furniture. Sensory organs located in the ears monitor your body’s motion and position in relation the gravity. Your vestibular sense enables you to keep your balance. If you spin around a few times in a circle, you feel dizzy because your brain is trying to compensate for the sensation.

perception Rules of perceptual organization, movement, depth perception, perceptual constancies, and visual illusions

Rules of perceptual organization CLOSURE Closure is the tendency to perceive a complete or whole figure even when there are gaps in what your senses tell you. Look at the pattern to the left. Do you see random blotches of ink or a dog sniffing the ground? If you see a dog, why? The answer is that you are familiar with dogs and that you try to fit the pieces of information into a familiar pattern.

Rules of perceptual organization, cont’d FIGURE-GROUND PERCEPTION Figure-ground perception is the perception of figures against a background. The image to the left is an example of this: you see either a vase or two profiles.

Other rules of organization Proximity is the nearness of objects or figures to each other. The law of similarity says that people think of similar objects as belonging together. The law of continuity says that people usually prefer to see smooth, continuous patterns rather than disrupted ones. The law of common fate says that people assume things have the same purpose when they are part of the same group.

movement Perception of movement Stroboscopic motion When we sense movement, we need to be able to make sense of it. To sense movement, humans need to see an object change its position relative to other objects. To observe that Earth moves around the sun, we would have to be somewhere in outer space. Stroboscopic motion is the illusion of movement is produced by showing the rapid progression of images or objects that are not moving at all. Movies are an example of this. Showing the frames in rapid succession creates the illusion of movement.

Depth perception Monocular cues for depth Monocular cues need only one eye to be perceived. Monocular cues cause certain objects in a piece of artwork to appear more distant from the viewer than others. Overlap is another monocular cue that tells us which objects are far away and which ones are near. Highlights, shadows, and texture gradients also play a part in this. Motion parallax is the tendency of objects to seem to move forward or backward depending on how far away they are from the viewer.

Depth perception, cont’d Whereas monocular cues can be perceived with just one eye, both eyes are required to perceive binocular cues for depth. Two binocular cues for depth are retinal disparity and convergence. Images will be slightly different because objects will be seen at different angles. This difference is referred to as retinal disparity. Convergence is associated with feelings of tension in the eye muscle. When we try to maintain a single image of an approaching image, our eyes must turn inward, or converge on it, giving us a cross-eyed look. Binocular Cues for Depth

Perceptual constancies Size constancy Color constancy Size constancy is the tendency to perceive an object as being of one size no matter how far away the object is. The image of a dog seen from a distance of 20 feet occupies about the same amount of space on the retina as an inch-long insect seen close up. Color constancy is the tendency to perceive objects as keeping their color even though different light might change the appearance of their color. If you enter a dark theater, all of the shirts have a grey hue, but you know that there are many different colors of clothing.

Perceptual constancies Shape constancy Brightness constancy Shape constancy—the knowledge that an item has only one shape no matter what angle you view it from. Ex. Looking at a cup from the top view or looking at a partially open door. Brightness constancy is the tendency to perceive an object as being equally bright even when the intensity of the light around it changes. We judge the brightness of an object by the brightness of other objects around it. For example, a black object really looks almost grey in very bright sunlight, but we perceive it as black because everything else around it is much brighter.

Visual illusions Do your eyes “play tricks on you”? Your brain can trick your eye through visual illusions. The rule of size constancy is that if two objects seem to be the same size and one is farther away, the farther object must be larger than it actually seems. Perhaps the converging lines strike you as receding into the distance. If so, you assume from experience that a horizontal line at the top is farther down the track— farther away from you.