Introduction

The topics of sensation and perception are among the oldest and most important in all of psychology. People are equipped with senses such as sight, hearing and taste that help us to take in the world around us. Amazingly, our senses can convert real-world information into electrical information that can be processed by the brain. The way we interpret this information– our perceptions– is what leads to our experiences of the world.

In this chapter, we will primarily focus on vision and hearing given the comparatively larger amount of research on these topics, but the other senses remain of great interest, especially because there is debate about what count as other “senses.” While taste, smell, and touch are typically agreed upon, consider that we also detect pain, temperature, bodily movement, and our sense of body in space.

Imagine standing on a city street corner. You might be struck by movement everywhere as cars and people go about their business, by the sound of a street musician’s melody or a horn honking in the distance, by the smell of exhaust fumes or of food being sold by a nearby vendor, and by the sensation of hard pavement under your feet.

In addressing how we take in and make sense of all the experiences mentioned above, it is probably best to start with one important distinction that can often be confusing: the difference between sensation and perception.

• The physical process during which our sensory organs—those involved with hearing and taste, for example—respond to external stimuli is called sensation. Sensation happens when you eat noodles or feel the wind on your face or hear a car horn honking in the distance.

• During sensation, our sense organs are engaging in transduction, the conversion of one form of energy into another. Physical energy such as light or a sound wave is converted into a form of energy the brain can understand: electrical stimulation.

• After our brain receives the electrical signals, we select, organize, and make sense of all this stimulation and begin to appreciate the complex world around us. This psychological process—making sense of the stimuli—is called perception. Perception of the same sense may vary from one person to another because each person’s brain interprets stimuli differently based on that person’s learning, memory, emotions, and expectations. It is during this process that you are able to identify a gas leak in your home or a song that reminds you of a specific afternoon spent with friends.

Signal Detection

Each sense organ—our eyes or tongue, for instance—requires a minimal amount of stimulation to detect a stimulus. This absolute threshold explains why you don’t smell the perfume someone is wearing in a classroom unless they are somewhat close to you. Because absolute threshold changes throughout the day and based on what other stimuli you have recently experienced, researchers define absolute threshold as the minimum amount of stimulation needed to detect a stimulus 50% of the time.

The way we measure absolute thresholds is by using a method called signal detection. This process involves presenting stimuli of varying intensities to a research participant to determine the level at which he or she can reliably detect stimulation in a given sense. During one type of hearing test, for example, a person listens to increasingly louder tones (starting from silence). Correctly indicating that a sound was heard is called a hit; failing to do so is called a miss. Additionally, indicating that a sound was heard when one was not played is called a false alarm, and correctly identifying when a sound was not played is a correct rejection. Alternatively, we might be more interested in whether someone can detect the difference between stimuli (sometimes referred to as the difference threshold or just noticeable difference) rather than the presence vs. absence of a stimulus.

One complicating factor here involves the idea of subliminal perception – can messages you are unaware of, embedded in movies or ads or the music playing in the grocery store, really influence what you buy? There is less evidence on that front, but it does appear that on a simpler level, stimuli presented outside of our conscious awareness can impact our behaviors. We will return to this topic in a later section.