We see a lemon as yellow because the pigments in the skin of a lemon reflect yellow light. The pigment absorbs all colors of light except yellow.

When it gets dark the cones lose their ability to respond to light. The rods continue to respond to available light, but since they cannot see color, so to speak, everything appears to be various shades of black and white and gray. that’s why It is difficult to distinguish between colors at night.

Why do you see a lemon as yellow? The lemon absorbs yellow wavelengths in the yellow region of the spectrum. The lemon might reflect only yellow wavelengths in the yellow region of the spectrum. The lemon reflects all wavelengths of light other than yellow.

Signal detection theory recognizes that the observer, whose physical and mental characteristics are always in flux, must compare a sensory experience with ever-changing expectations and biological conditions.

The absolute threshold is the minimum amount of stimulation required for a person to detect the stimulus 50 percent of the time. The difference threshold is sometimes called the just noticeable difference (jnd), and it depends on the strength of the stimulus.

As it relates to psychology, transduction refers to changing physical energy into electrical signals (neural impusles) that can make their way to the brain.

Early sensory psychophysics studies by Weber and Fechner showed that sensory systems always transmit four basic types of information: modality, location, intensity and timing.

Light enters the visual system through the eye and strikes the retina at the back of it. The retina is composed of specialized cells, the rods and cones, which convert light energy into neural activity. When light strikes these pigments, they change form, causing a cascade of chemical reactions in these photoreceptors.

Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 30 minutes, after which rods are more sensitive. Rhodopsin was discovered by Franz Christian Boll in 1876.

Exposure of the retina to light hyperpolarizes the rods and cones and removes their inhibition of bipolar cells. The now active bipolar cells in turn stimulate the ganglion cells, which send action potentials along their axons (which leave the eye as the optic nerve).

Perception

The human eye and brain together translate light into color. Light receptors within the eye transmit messages to the brain, which produces the familiar sensations of color. Rather, the surface of an object reflects some colors and absorbs all the others. We perceive only the reflected colors.

The color or hue of light depends on its wavelength, the distance between the peaks of its waves. The brightness of light is related to intensity or the amount of light an object emits or reflects. Brightness depends on light wave amplitude, the height of light waves.

How We Perceive Sound

• First Step: Sound waves travel through the outer ear.
• Second Step: The vibration of the ear drum initiates movement of the three ear bones.
• Third Step: The stapes then transmits the mechanical energy (carried by the bones) into the inner ear in the form of hydraulic energy.

Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.

Sound is produced when an object vibrates, creating a pressure wave. This pressure wave causes particles in the surrounding medium (air, water, or solid) to have vibrational motion. As the particles vibrate, they move nearby particles, transmitting the sound further through the medium.

Sound waves move by vibrating objects and these objects vibrate other surrounding objects, carrying the sound along. The further away from the original source of a sound you are, the waves lessen until they don’t have the strength to vibrate any other particles.

When a drum is hit, the air particles next to the drum skin vibrate and collide with other particles, and this vibration is then transmitted through the air. This is known as wave compression, which allows sound to travel quickly through the air.

While sound moves at a much faster speed in the water than in air , the distance that sound waves travel is primarily dependent upon ocean temperature and pressure.