An illustration of the visible light spectrum can demonstrate the relationship between a wave's physical properties and its perceived color. Such a diagram typically shows a series of colored waves, often from red to blue. The red wave is depicted with the longest wavelength and, consequently, the lowest frequency. As one moves through the spectrum towards the blue wave, the wavelengths progressively shorten, and the frequencies increase, visually confirming the inverse relationship between wavelength and frequency as it applies to light.

Visual Representation of Wavelength, Frequency, and Color

For humans, the visible spectrum is the portion of the electromagnetic spectrum that human eyes can see. It is associated with wavelengths from about $$380$$ to $$740$$ nanometers (nm), where a nanometer is one billionth of a meter.

The Human Visible Spectrum

An observer is shown two distinct light sources. Light Source A emits a bright blue light, while Light Source B emits a dim red light. How do the physical properties of the light waves from Source A compare to those from Source B?

In human vision, the physical properties of a light wave directly determine our perceptual experience. The wavelength of a light wave is perceived as its color (or hue), while its amplitude determines the perceived intensity or brightness of that light.

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The two types of waves for perception are: 

1. Light Waves (Visual Stimuli) 
2. Sound Waves (Auditory Waves) 

Types of Waves

The electromagnetic spectrum is the complete range of electromagnetic radiation in the environment. It includes gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves.

Classification of the Electromagnetic Spectrum

Visual stimuli (light) and auditory stimuli (sound) are both transmitted as wave forms. These waves are defined by specific physical characteristics, most notably their amplitude, wavelength, and timbre.

Physical Characteristics of Waves in Sensation and Perception

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Relationship Between Physical Properties of Light and Visual Perception

In human audition, a sound wave's physical characteristics directly correspond to specific psychological perceptions. The frequency of a sound wave is experienced as its pitch, whereas the amplitude of the wave is experienced as its loudness.

Relationship Between Physical Properties of Sound Waves and Auditory Perception

An electromagnetic-spectrum diagram can compare radiation types by wavelength, frequency, and object-size scale. In the illustrated scale, wavelength increases from gamma rays at $${}10^{-12}$$ meters through X-rays at $${}10^{-10}$$ meters, ultraviolet at $${}10^{-8}$$ meters, visible light at $${}0.5 \times 10^{-6}$$ meters, infrared at $${}10^{-5}$$ meters, microwaves at $${}10^{-2}$$ meters, and radio waves at $${}10^3$$ meters. Across the same scale, the frequency labels decrease from $${}10^{20}$$ to $${}10^4$$ hertz, and the size comparison ranges from atomic nuclei to buildings.

Visual Representation of the Electromagnetic Spectrum

Some species can detect portions of the electromagnetic spectrum outside the human visible range. For example, honeybees can see ultraviolet light, and some snakes can detect infrared radiation in addition to typical visual light cues.

Nonhuman Detection of the Electromagnetic Spectrum

The amplitude of a wave is defined as the distance measured from the wave's central line to either the highest point of its crest or the lowest point of its trough.

Wave Amplitude

The wavelength is the length of the wave from one peak to the next.

Wavelength

A standard diagram of a wave depicts it as an oscillating line moving equally above and below a central horizontal axis. The highest points on this line are the crests, and the lowest points are the troughs. The horizontal distance between two consecutive peaks is labeled as the wavelength, while the vertical distance from the central axis to a crest or a trough is labeled as the amplitude.

Visual Representation of a Wave

Timbre is the perceptual quality that allows listeners to distinguish between different sounds, even when those sounds have the same pitch (frequency) and loudness (amplitude). Described as a sound's purity or character, timbre is determined by the complex interplay of a sound wave's frequency, amplitude, and timing. This quality explains why different musical instruments playing an identical note at the same volume still sound distinct from one another.

Timbre as a Perceptual Quality of Sound

Consider two light waves, Wave A and Wave B. Wave B has a greater amplitude (height) and a longer wavelength (distance between peaks) than Wave A. How would the light from Wave B be perceived compared to the light from Wave A?

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