• Define sensation
• Define perception

Sensation and Perception

You have probably known from a young age that we have five senses: vision, hearing (audition), smell (olfaction), taste (gustation), and touch (somatosensation). It turns out that this notion of five senses is oversimplified—we also have sensory systems that provide information about balance (the vestibular sense), body position and movement (proprioception and kinesthesia), pain (nociception), and temperature (thermoception).

What Is Sensation?

 

 

sensation

Sensation occurs when specialized neurons called sensory receptors respond to specific kinds of stimuli in our environment.

 

When sensory information is detected by these receptors, a sensation has taken place.

This sensory input is then converted into electrical signals (action potentials) that travel to the central nervous system for processing—a process called transduction. In other words, transduction transforms physical energy (like light waves or sound vibrations) into neural messages that your brain can interpret.

Thresholds of Sensation

Not all stimuli are strong enough for us to detect. Psychologists use several key concepts to explain our sensory limits.

absolute threshold

Absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. Another way to think about this is by asking how dim can a light be or how soft can a sound be and still be detected half of the time.

A stimulus reaches a physiological threshold when it is strong enough to excite sensory receptors and send nerve impulses to the brain: this is an absolute threshold.

The sensitivity of our sensory receptors can be quite amazing. It has been estimated that on a clear night, the most sensitive sensory cells in the back of the eye can detect a candle flame 30 miles away (Okawa & Sampath, 2007). Under quiet conditions, the hair cells (the receptor cells of the inner ear) can detect the tick of a clock 20 feet away (Galanter, 1962).

Below Awareness: Subliminal Messages

Sometimes, stimuli are presented below the threshold of conscious awareness—these are called subliminal messages.

subliminal messages

Subliminal messages register below the threshold—they are not strong enough to excite sensory receptors and send nerve impulses to the brain. The message is received, but we are not consciously aware of it, and for whatever reason, it has not been selected for processing in working or short-term memory.

Over the years, subliminal messages have been a source of fascination in advertising, music, and self-help media.

Research shows that people can process and even respond to some information outside of awareness, but these effects are typically very small and short-lived. Hidden messages do not control behavior (Kunst-Wilson & Zajonc, 1980; Rensink, 2004; Nelson, 2008; Radel et al., 2009; Loersch, Durso, & Petty, 2013).

Dig Deeper: Nonconscious^[1] Perception

Much of our mental processing happens nonconsciously—that is, while we are awake but unaware of it.

For example, we can form attitudes toward things simply through repeated exposure, even without realizing it. This phenomenon is known as the mere exposure effect (Zajonc, 1968).

People often develop positive feelings toward stimuli they’ve encountered multiple times, even when those exposures were subliminal or extremely brief (Kunst-Wilson & Zajonc, 1980).

Absolute thresholds are generally measured under incredibly controlled conditions in situations that are optimal for sensitivity. Sometimes, we are more interested in how much difference in stimuli is required to detect a difference between them.

just noticeable difference (jnd) or difference threshold

Just noticeable difference (jnd) or difference threshold is the difference in stimuli required to detect a difference between them.

Unlike the absolute threshold, the difference threshold changes depending on the stimulus intensity. While there are estimations of humans’ ability to detect differences in stimuli, the jnd can differ between individuals.

For instance, a phone lighting up in a dark theater is obvious, but in a brightly lit gym, the same phone might go unnoticed.

The brightness doesn’t change—but our ability to detect it does.

Ernst Weber proposed this theory of change in difference threshold in the 1830s, and it has become known as Weber’s law.

Weber’s law

Weber’s law states that the difference threshold is a constant fraction of the original stimulus; it is the idea that bigger stimuli require larger differences to be noticed.

For example, you might easily tell the difference between 1 and 2 pounds, but not between 10 and 11 pounds

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