Sensory Organs and Mechanisms - AP Psychology

The just noticeable difference is the minimum value in which a change in a sensory stimulus may still be detected. An example of this would be if an observer could tell the difference in the brightness in a room of 20 lit light-bulbs if 5 were dimmed at once, but not if fewer were.

Weber's law describes how changes in the just noticeable difference are proportional to changes in the magnitude of that stimulus. For example, to use the previous case of the room and light-bulbs, if the just noticeable difference in a room of 20 lights was five bulbs, then the just noticeable difference in a room of 40 illuminated light bulbs should be 10. They have increased by a factor of two.

The absolute threshold is the minimum value of a stimulus that is sufficient to be detected. This is different from the just noticeable difference in that it is not addressing changes in a stimulus, but merely the detection of that stimulus itself.

Accommodation describes the way in which the eyes will adjust to keep an object in focus depending on its proximity. This does not have to do with just noticeable changes in a stimulus.

The optic nerve leaves the eye through the blind spot, in the rear of the eye. The retina is interrupted in this region by the outflow of nerves carrying visual information to the brain. As such, it is devoid of photoreceptive cells, and no light is detected here. As a result of this, no visual information is generated by this region, and it is in effect, a blind spot.

The lens is the crystalline structure which focuses light entering the eye onto the retina, and is located in the front of the eye.

The cornea is the transparent layer forming the front of the eye. The sclera is the firm, white, outer layer of the eye.

The vestibular sense is that which controls our sense of balance and orientation. It is produced as a result of movement sensitive receptor cells in fluid filled chambers within the inner ear called the semi-circular canals. Changes in the body's orientation in space cause this fluid to move, as it seeks to find its level under the affect of gravity. This movement is detected by the hair-like receptor cells within the semi-circular canals, which send signals to the brain.

As a result of this sense, we are aware of our balance, and are able to stand upright and move without falling over.

Pain receptors in the skin help keep us away from injurious stimuli, and the olfactory sense helps us to avoid noxious stimuli.

Hormones and physical factors help prevent us from overeating, and the pupil and pain receptors in the eye help keep us from staring directly into the sun- that and hopefully common sense!

The minimum amount of energy for a stimulus to be registered as a sensation is known as the absolute threshold. Any stimulus that occurs too weakly to surpass this threshold will not result in a sensation, and will thus be undetected.

The just noticeable difference refers to the minimum amount of change in a stimulus necessary for a difference in its intensity to be recognized.

Transduction is the conversion of energy from one form into another, for example, from light energy into electrical energy during vision.

The minimum threshold may sound like the correct answer, but it is in fact not the correct term. The absolute threshold is the appropriate label for the phenomenon.

The electromagnetic spectrum is comprised of energies of many different wavelengths and frequencies, among which are gamma, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves. The human eye is capable of interpreting visual information carried in the frequency range of visible light. Some other species may perceive in ultraviolet or infrared frequencies as well.

None of the other options listed provide examples of the electromagnetic spectrum.

Audition is the sense of hearing. When we hear a sound, we are in fact detecting vibrations in the environment caused by sound pressure waves. The frequencies of these vibrations are converted into electrical information within the cochlea of the inner ear, and give rise to the sensation of sound by the brain.

Tactile pressure and other tactile stimuli would be detected by skin receptors throughout the body.

The eyes detect visible light, a component of the electromagnetic spectrum.

Audio waves is not the correct term for sound waves.

Hyperopia, or farsightedness, is a condition of the eye in which a person cannot "focus on near objects." They are able to perceive distant objects without difficulty, but objects nearby will appear blurry and out of focus. This is in contrast to myopia, in which distant objects appear blurry, and near ones clear.

Hyperopia has no impact on the perception of color. It is easily treated through corrective lenses or LASIK.

The iris is the colored center portion of the surface of the eye that controls the expansion and constriction of the pupil. This is done to allow more light into the eye in dim lighting conditions, and to restrict light from coming into the eye in bright lighting conditions. As a result, the iris controls the "diameter of the pupil," and how much light enters the eye.

The iris does not control the shape of the lens. This is performed by the ciliary muscles, which focus the lens by changing its shape. The sensitivity of the retina to light does not change aside from injury or damage.

Visual acuity is best for light falling upon the fovea. The fovea is an area of the retina corresponding to the center of our visual field. In other words, any object we focus our eyes on will be reflecting light that is striking our fovea. This region contains the highest concentration of cones, which are more sensitive than rods, and produce more detailed visual information.

Visual acuity diminishes towards the periphery of the retina and visual field, as more rods and fewer cones are responsible for processing light information in these regions.

The blind spot receives no visual information whatsoever, as no photoreceptors are present here. Instead, the optic nerve interrupts the retina and exits the back of the eye in this location.

Transduction is an essential stage of perception. This is when energy is converted from one form into another: namely, from light, chemical, or physical energy from incoming stimuli into electrical energy within the nervous system. Without this key step, perception as we know it would be impossible. To name a few examples, this process occurs with in the retina of the eyes, within the cochlea of the inner ears, within the olfactory receptors of the nose, and within gustatory receptors within taste buds on the tongue.

Transduction does not involve the amplification of energies; furthermore, it does not involve screening or analysis of information for any specific purposes. This occurs at the level of the brain, not within receptor cells, where transduction occurs.

Focusing is accomplished by adjusting the thickness of the lens. This action is performed by the ciliary muscles. By changing the shape of the lens, light entering the eye from different focal points is brought into alignment on the retina, allowing for a clear image.

The pupils control the amount of light entering the eye, but do not contribute to focusing. Thus dilating or constricting the pupils has no effect on focus. Furthermore, these actions are outside of conscious control, while focusing may be performed consciously.

The thickness of the cornea does not change under normal circumstances, and does not play a role in focusing. Likewise, the distance between the lens and the retina does not change under normal circumstances, and is not a movement performed by the eye.

Every visual field has a blind spot, where there are no rods and cones (known as photoreceptors) to detect external images. Our brain uses context clues from the environment to help fill in this blind spot to make a complete picture. The blind spot is located on the optic disk, which is the location where the optic nerve exits the back of the eye. Due to the nerve tissue in this spot, there are no photoreceptors to detect input.

In contrast, the fovea centralis is the region of the retina with the highest concentration of cones.

Humans have about 100 to 125 million rods in the retina, but only about 5 to 6.4 million cones. The fovea only contains cones—no rods. In the remainder of the retina, rods vastly outnumber cones.

The human retina has two types of cells that respond to light: cones and rods. Rods are more numerous, but can only detect light and dark shades. Cones respond to different wavelenghts of light, and can thus transmit color information. They are highly concentrated in the fovea of the retina.

Over time, a constant stimulus in the environment evokes less and less of a response from one's sensory system. Sensory neurons respond at first to these stimuli, but over time they stop responding in order to focus attention on other stimuli in the environment.

The stages of cognitive development, according to Jean Piaget, are the sensorimotor, preoperational, concrete operational, and formal operational. During the sensorimotor stage, the period between birth and age two, cognitive development is limited to motor responses caused by sensory stimuli.

Between ages two and six—the preoperational stage—the child learns to use language. Between ages seven and eleven—the concrete operational stage—children begin thinking logically. During the formal operational stage, age twelve through adulthood, people develop the ability to think about abstract concepts such as deductive reasoning.

The iris is a ring of muscle tissue that forms the colored part of the eye. Additionally, the iris controls the size of the pupil opening, and thus controls how much light enters the eye.

The retina contains the rods and the cones, which are sensitive to light that enters through the pupil. Rods are able to detect shades of dark and light, while cones are able to detect color. When light strikes these cells, it is converted into electrical neural impulses that are transmitted through the optic nerve to the brain.

The middle ear contains three tiny bones: the malleus (hammer), the incus (anvil), and the stapes (stirrup). These bones concentrate the vibrations coming from the eardrum, and send these signals to the cochlea's oval window.

Each region of the ear uses a different medium to transmit vibrations. Remember that the outer ear uses air as the medium (sound waves impact the ear drum). The middle ear uses bones to transmit these vibrations to the oval window. Finally, the inner ear uses fluid found in the cochlea to transmit the vibrations to neural tissue.