Additionally, one teaspoon of sugar can be tasted within two gallons of water, and the human olfactory system can detect the scent of one drop of perfume throughout a six room apartment. 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). 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). The sensitivity of our sensory receptors can be quite amazing. 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. Absolute threshold refers to the minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. The sensitivity of a given sensory system to the relevant stimuli can be expressed as an absolute threshold. Touch is particularly interesting because it is made up of responses from many different types of receptors found within the skin that send signals to the central nervous system in response to temperature, pressure, vibration, and disruption of the skin such as stretching and tearing.įree nerve endings embedded in the skin that allow humans to perceive the various differences in our immediate environment. The vision system absorbs light using rod and cone receptors located at the back of the eyes, sound is translated via tiny hair like receptors known as cilia inside the inner ear, smell and taste work together most of the time to absorb chemicals found in airborne particles and food via chemically sensitive cilia in the nasal cavity and clusters of chemical receptors on the tongue. 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), and each one of these sensory systems has different receptors tuned to transduce different stimuli. It turns out that this notion of five senses is extremely oversimplified. You have probably known since elementary school that we have five senses: vision, hearing (audition), smell (olfaction), taste (gustation), and touch (somatosensation). Throughout this chapter sensations and perceptions will be discussed as separate events, whereas in reality, sensations and perceptions can be more accurately thought of as occurring along a continued where boundaries are more fluent between where a sensation ends and a perception begins. Also, a sensation would be hearing a loud, shrill tone, whereas a perception would be the classification and understanding of that sounds as a fire alarm. Sensations allow us to see a red burner, but perceptions entail the understanding and representation of the characteristic hot. In order for sensations to be useful, we must first add meaning to those sensations, which create our perceptions of those sensations. Perceptions on the other hand, require organizing and understanding the incoming sensation information. Sensations allow organisms to sense a face, and smell smoke when there is a fire. Transduction represents the first step toward perception and is a translation process where different types of cells react to stimuli creating a signal processed by the central nervous system resulting in what we experience as a sensations. The conversion from sensory stimulus energy to action potential is known as transduction. These cells relay messages, in the form of action potentials (as you learned when studying biopsychology), to the central nervous system. For example, light that enters the eye causes chemical changes in cells that line the back of the eye. When sensory information is detected by a sensory receptor, sensation has occurred. What does it mean to sense something? Sensory receptors are specialized neurons that respond to specific types of stimuli. Discuss the roles attention, motivation, and sensory adaptation play in perception.Describe the concepts of absolute threshold and difference threshold.Distinguish between sensation and perception.By the end of this section, you will be able to:
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