Rick Rubenstein asks
Has there been any research done on the familiar phenomenon wherein a word which is repeated over and over begins to look misspelled, or even like complete gibberish?
Yes, lots. The phenomenon was described by Edward Tichener in A Beginner's Psychology, 1915:
Repeat aloud some word — the first that occurs to you; house, for instance — over and over again; presently the sound of the word becomes meaningless and blank; you are puzzled and a morsel frightened as you hear it.
The earliest serious study known to me is M.F. Bassett and C.J. Warne, "On the Lapse of Verbal Memory with Repetition" (Minor Studies from the Psychological Laboratory of Cornell University XLIV), The American Journal of Psychology 30(4) 1919:
It is well known that if a familiar word be stared at for a time, or repeated aloud over and over again, the meaning drops away. In this paper we report the result of experiments whose aim was the determination of the number of repetitions required for monosyllabic nouns to lose their meaning.
The terms "verbal satiation" and "semantic satiation" came to be used to refer to this loss of meaningfulness. Thus Donald Smith and Alton Raygor, "Verbal satiation and personality", Journal of Abnormal and Social Psychology, 52(3) 1956:
Satiation may be described as the reduction in effectiveness of a stimulus with continued exposure. The concept has been invoked to account for a number of diverse phenomena, loss of word meaning with repetition, visual alternation during fixation of ambiguous figures, boredom, alternation behavior of rats in a T maze, and diagnosis of brain lesion.
Wallace Lambert and Leon Jakobovits proposed a clever way to measure (and to conceptualize) this change "(Verbal satiation and changes in the intensity of meaning", Journal of Experimental Psychology 60(6) 1960):
Several investigators have demonstrated that Ss experience a change or loss of meaning for words which have continuously repeated or fixated for a certain period of time. For instance, Bassett and Warne (1919) reported that the meanings of familiar nouns which were repeated aloud "dissipated" for their Ss within 3 or 4 sec. More recently, it was found that if Ss fixated a word exposed on a screen for 20 sec., their first association to the word is uncommon as measured by the Kent-Rosanoff Word Association Test (Smith & Raygor, 1956). […] Before the ful implication of this concept for theories of learning and meaning can be determined, it is necessary to develop a method for reliably measuring the extent of meaning change which be attributed to the satiation experience. […]
Osgood, Suci, and Tannenbaum (1957) have proposed an objective and reliable instrument for the measurement of certain aspects of connotative meaning. This instrument, the "semantic differential," consists of a series of scales each representing a 7-point, bipolar dimension. The meaning of a word, such as "father," is given by its position on an evaluative factor (its degree of goodness or badness), on an activity factor, and on a potency factor. The theory underlying this method assumes that the meaning of a word has a place in a multidimensional semantic space. A word without meaning would rest at the point of origin for all dimensions. […]
In the present studies, the semantic differential is used as a method of indexing changes in meaning induced by means of verbal repetition of words.
They found that after saying a word aloud 2-3 times per second for 15 seconds, subjects' estimates of its position in this semantic space moved to a point nearer the origin. A corresponding period of silence had almost no effect, and repeating a different word had a much smaller (and not statistically significant) effect.
There's a different, but perhaps related, effect that was first described by Richard Warren. In "Verbal transformation effect and auditory perceptual mechanisms", chapter XVIII in Norman Lass, Ed., Speech and hearing science: selected readings (Volume 10), 1974, he wrote:
If, rather than repeating a word to oneself, one listens to a recording of a word repeated over and over, a different effect occurs. Abrupt illusory changes are experienced, frequently involving considerable phonetic distortion. It is usually difficult to believe that the stimulus is not changing, even when the listener knows that all repetitions are identical. This "verbal transformation effect" has revealed some rather unexpected characteristics of speech perception and has suggested mechanisms underlying the perception of connected discourse.
Here's his description of his first experiment:
The first systematic study of the VT effect employed British sailors as subjects (Warren, 1961a). Stimuli were prepared by recording single vocal statements which were then spliced to form a loop of tape. Each loop was played back and rerecorded on a conventional reel to give a sitmulus which could be played for 3 minutes. […]
The subject listened to the repeated stimulus through headphones, tapping on the table and calling out what he heard as soon as he could […]
An example of one subject's responses to […] TRESS, played loudly and clearly for 3 minutes is as follows (all responses listed in the order reported): "stress, dress, stress, dress, Jewish, Joyce, dress, Jewess, Jewish, dress, floris, florist, Joyce, dress, stress, dress, purse."
You can find plenty of other research reports by searching Google Scholar for "verbal satiation", "semantic satiation", or "verbal transformation effect". A small and somewhat random sample of the hits:
Lee Smith and Raymond Klein, "Evidence for semantic satiation: Repeating a category slows subsequent semantic processing", Journal of Experimental Psychology: Learning, Memory, and Cognition, 16(5) 1990.
M Pilotti et al., "The effect of presemantic acoustic adaptation on semantic 'satiation'", Mem Cognit 25(3) 1997.
T Ditzinger, B. Tuller, and J.A.S. Kelso, "Temporal patterning in an auditory illusion: the verbal transformation effect", Biological Cybernetics 77(1) 1997.
Anahita Basirat et al., "Parieto-frontal gamma band activity during the perceptual emergence of speech forms", Neuroimage 42(1) 2008.