Perception

Perception refers to any kind of conscious sensory experience whereby external stimuli generate electrical signals in the nervous system of an organism that ultimately allow some kind of interaction with the environment. In human communication, the external stimulus is usually a spoken acoustic signal, and the receiving organism is typically a human listener. The auditory system of the listener transduces this sound into neural impulses in the brain, which are then processed at several stages. The traditional view of speech perception is that the acoustic signal from a speaker is perceived as a sequence of consonants and vowels which are further organized into words and sentences. However, the acoustic waveform contains information about not only basic linguistic elements but also nonlinguistic properties such as the speaker’s location in space; the identity of the speaker including size, gender, and place of origin; the speaker’s emotional state; and even the acoustic environment in which he or she is speaking, such as the size of the room and the acoustic reflectivity of nearby surfaces. However, communication can also include sign language and lipreading, which rely on both the visual system and the Tadoma method in which an individual who is deafBlind uses tactile information to perceive the movement of the speaker’s lips and jaw to understand speech.

In general, perception depends not only on the external stimulus itself but also on the experiences of the receiver as a result of learning, attention, [Page 1336]expectation, and the wider context in which the stimulus occurs. Perceptual systems also interact with one another: Speech perception is modulated not only by the sound of the speech arriving at the ear of the listener but also by the image of the speaker’s lips moving in synchrony. Similarly, the tactile sensation of a puff of air on the listener’s face can even change the perception of a speech sound from /ba/ to /pa/. This entry provides an overview of perception with a particular emphasis on speech perception, including how it works, the similarities between different modalities of perception, and specific phenomena related to contrast effects, learning, and top-down effects.