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
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.
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These results indicate a grave deterioration of verbal skills
Spontaneous Speech
Sparse, marred by frequent anomia, verbal perseverations, and neologisms
Oral Naming
Word Comprehension
- Oldfield picture naming
- Easy category naming
- 9/30 (very poor)
- 24/40 (very poor)
Reading, Writing, and Repetition
- Word-picture matching
- 39/40
Thus, she demonstrated severe naming difficulties with relatively preserved comprehension, reading, writing, and repetition skills
- Reading aloud
- Writing to dictation
- Repetition
- 39/40
- 37/40
- 40/40
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).
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.
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).
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.
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).
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.
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.
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.
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.
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