The Effect of Rate of Presentation and Repetition on Verbal Perseverations in Aphasia: Implications for Priming Accounts

Stephen J. Gotts
Dept. of Psychology, Carnegie Mellon University
& Center for the Neural Basis of Cognition, Pittsburgh, PA

Antonio Incisa della Rocchetta and Lisa Cipolotti
Dept. of Neuropsychology, National Hospital for Neurology and Neurosurgery, London, England



Introduction

A verbal recurrent perseveration is the inappropriate repetition of a recent utterance when a different response is expected (Sandson & Albert, 1984).

Several accounts have suggested that these perseverations result when processing is too weak or slow to dominate a recently primed response (e.g. Cohen & Dehaene, 1998; Martin et al., 1998; Plaut & Shallice, 1993).

On these accounts, factors which influence either the "strength" of the stimulus or the "strength" of priming might also be expected to influence the occurrence of perseverations:

  • rate of presentation
  • repetition
  • lexical frequency
  • semantic relatedness



  • Case Report

    The patient (EB) is a 71-yr-old, right-handed homemaker suffering from a malignant left fronto-temporal meningioma.

    MRI scan: Brodmann's areas unequivocally involved were: 44, 45, 46, 10, 22, and 6.




    Intellectual and Memory Assessment: Scores


    VIQ
    Raven's Colored Matrices
    Recognition Memory for Faces
    59 (defective)
    26/36 (75 %-ile)
    16/25
    These results indicate a grave deterioration of verbal skills



    Language Assessment


    Spontaneous Speech

    Sparse, marred by frequent anomia, verbal perseverations, and neologisms

    Oral Naming
    Oldfield picture naming
    Easy category naming
    9/30 (very poor)
    24/40 (very poor)
    Word Comprehension
    Word-picture matching
    39/40
    Reading, Writing, and Repetition
    Reading aloud
    Writing to dictation
    Repetition
    39/40
    37/40
    40/40
    Thus, she demonstrated severe naming difficulties with relatively preserved comprehension, reading, writing, and repetition skills



    Experiment 1: Rate, Repetition, Frequency, and Semantic Relatedness


    EB showed severe anomia and recurrent perseverations only in naming tasks. What factors were influencing her naming skills?

  • We investigated the effects of presentation rate, repetition, frequency, and semantic relatedness on picture naming.

  • The patient saw 4 pictures presented one at a time in a single block of trials.

  • Within a block, each picture was presented twice in a pseudorandom order.

  • Half of blocks involved objects with high frequency names and half with low frequency names.

  • Crossed with frequency was semantic relatedness. Half of the blocks involved semantically close objects and half semantically distant objects.

  • Two rates of presentation were used with each block: fast (response-stimulus interval, RSI = 1 sec) and slow (RSI = 15 sec).




  • Experiment 1: Results



    EB showed a significant rate effect. However, rate did not have an effect on perseverations.

    EB showed a significant frequency effect. There were more perseverations and omissions in the low frequency condition.

    No significant effects of repetition or semantic relatedness were found.




    Experiment 2: Rate, Repetition, and Semantic Relatedness


    We attempted to replicate some of the results of Exp. 1.

  • In a block of trials, the patient saw 6 pictures presented in array format, but probed for naming one at a time.

  • Within a block, each picture was presented twice in a pseudorandom order.

  • Half of blocks involved semantically close objects and half semantically distant objects.

  • Two rates of presentation were used with each block: fast (RSI = 1 sec) and slow (RSI = 10 sec).




  • Experiment 2: Results



    EB showed a significant rate effect. There were more omissions but not more perseverations in the fast rate condition.

    EB showed a significant repetition effect. There were more perseverations following within-block repetition.

    There were significantly more perseverations in the semantically close than in the semantically distant arrays.




    Experiment 3: Repetition and Semantic Relatedness


    We attempted to resolve two discrepancies between the results of Exp. 1 and 2: the effect of repetition and semantic relatedness on perseverations. Both of these effects were absent in Exp. 1 but present in Exp. 2.

  • The patient saw 3 pictures presented one at a time in a single block of trials.

  • Within a block, each picture was presented twice in a pseudorandom order.

  • Half of blocks involved semantically distant objects (within-category) and half semantically very distant objects (between-category).




  • Experiment 3: Results



    EB showed a significant repetition effect. There were more perseverations following within-block repetition.

    There were no effects of semantic relatedness. Thus, the influence of semantic relatedness on EB's naming performance is weak at best.




    Perseverations: A "Spacing" Effect


    The lack of a rate effect in perseverations is counter to findings from a group study of aphasic patients (Santo Pietro & Rigrodsky, 1982).
    Is there no decay in EB's tendency to perseverate?

    "Lag" in time (seconds) between a response and its subsequent perseveration can show how the tendency to perseverate "decays" (see also Cohen & Dehaene, 1998):





    These graphs show a "spacing effect" in perseverations: When repetitions are spaced far apart in time, "decay" is slower.




    Discussion


  • Consistent with existing priming accounts or perseveration, EB was more likely to perseverate following repetition and to pictures with low frequency names.

  • The lack of a semantic relatedness effect in perseverations is not necessarily inconsistent with existing accounts. This null effect along with EB's preserved comprehension and the available neuroanatomical evidence suggests a post-semantic impairment.

  • However, EB was not more likely to perseverate with a fast presentation rate.

  • We also observed a "spacing effect" in EB's perseverations: Her tendency to perseverate decayed more slowly when stimuli were presented at a slow rate.

  • The complex relationship between rate and perseveration is not predicted by existing accounts, and thus requires further specification.


  • What might explain our pattern of results?

  • Recent ideas about the neural basis of priming suggest that faster processing results from a reduction in the activity of irrelevant information rather than residual activity of relevant information (Desimone, 1996).

  • Neurons commonly show reduced activity under repeated stimulation. Interestingly, a spacing effect has also been observed: The reduction in activity "recovers" more slowly when repetitions are spaced apart in time (Byrne, 1982; Wang & Kaczmarek, 1998).

  • If irrelevant information recovers from its reduced state at a slower rate when repetitions are spaced further apart, then priming will last for a longer period of time.

  • This lengthened priming effect under a slow presentation rate will then allow primed responses to continue to dominate current inputs which are weak or slow, producing perseverations. Hence, a spacing effect would be observed in perseverations.




  • References


    Byrne, J.H. (1982). Analysis of the synaptic depression contributing to habituation of gill-withdrawal reflex in Aplysia californica. Journal of Neurophysiology, 48, 431-438.

    Cohen, L. & Dehaene, S. (1998). Competition between past and present: Assessment and interpretation of verbal perseverations. Brain, 121, 1641-1659.

    Desimone, R. (1996). Neural mechanisms for visual memory and their role in attention. Proceedings of the National Academy of Sciences - USA, 93, 13494-13499.

    Martin, N., Roach, A., Brecher, A., & Lowery, J. (1998). Lexical retrieval mechanisms underlying whole-word perseveration errors in anomic aphasia. Aphasiology, 12, 319-333.

    Plaut, D.C. & Shallice, T. (1993). Perseverative and semantic influences on visual object naming errors in optic aphasia: A connectionist account. Journal of Cognitive Neuroscience, 5, 89-117.

    Sandson, J. & Albert, M.L. (1987). Perseveration in behavioral neurology. Neurology, 37, 1736-1741.

    Santo Pietro, M.J. & Rigrodsky, S. (1982). The effects of temporal and semantic conditions on the occurrence of the error response of perseveration in adult aphasics. Journal of Speech and Hearing Research, 25, 184-192.

    Staddon, J.E.R. & Higa, J.J. (1996). Multiple time scales in simple habituation. Psychological Review, 103, 720-733.

    Wang, L-Y. & Kaczmarek, L.K. (1998). High-frequency firing helps replentish the readily releasable pool of synaptic vesicles. Nature, 394, 384-388.



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    This page last updated 3 June 1999.