Amusia: disorders involving music. There are many forms of amusia as there are many elements involved (in music), all concerned with the perception, decoding, and synthesis of sound and time. (Sacks, 99)
Cognitive disorder of “auditory perception” characterized by a reduced ability to perceive information contained in auditory stimuli despite intact “auditory pathways.” Affected individuals have difficulty with speech perception, sound localization, and comprehending the meaning of “inflections” of speech. (MeSH) (Some) patients can hear “timbre” and “rhythm” but not “melody” or vice versa. (Levitin, 194) Also referred to as ‘congenital amusia’ and ‘auditory perceptual disorder.’
Rhythm Deafness: inability to understand rhythm. (May be) slight or profound, congenital or acquired. Forms of rhythm deafness are rarely total, because rhythm is represented widely in the brain. (Sacks, 99)
Tone Deafness: better labeled ‘tune deafness,’ people with this condition (about 3% of the population) have normal hearing and can usually discriminate between musical notes perfectly well that is, if they are presented with one note after another they can tell if (the notes) are the same or different. Where they struggle is in making those judgments based on knowledge of the structure of the melody or tune. They may be completely unable to detect a note of the wrong pitch in the context of a familiar melody. EEG recordings can detect a rapid and reliable response to a misplaced note… but (not to) a second signal that occurs slightly later, in frontal regions (of the brain), which correlates with conscious awareness of that wrong note. Usually characterized by an inability to recognize familiar tunes from the melody alone (without lyrics) and, not surprisingly, difficultires in singing in tune. (Mitchell, 142) People with such an amusia can veer off key without realizing it, or be unable to recognize off-key singing by others. (Sacks, 100) A psychologist discovered a patient who has absolute pitch but is tone deaf. He can name notes perfectly, but he cannot sing. (Levitin, 184)
Total Amusia: tones are not recognized as tones, and music therefore, is not experienced as music. (In a) case in the neurological literature (the authors) describe one man, a former singer, who complained of hearing a screeching car whenever he heard music. (Sacks, 101)