تمارض، مربیگری و اثر موقعیت زنجیره ای

The normal pattern of performance on list-learning tasks is to recall more words from the beginning (primacy) and end (recency) of the list. This pattern is also seen in patients with closed head injury, but malingerers tend to recall less words from the beginning of word lists, leading to a suppressed primacy effect. The present study examined this pattern on both learning trials and delayed recall of the Auditory Verbal Learning Test (AVLT) in 34 persons performing with normal effort, 38 naive malingerers, 33 warned malingerers, and 29 head-injured patients. Both malingering groups had lower scores on the primacy portion of the list during learning trials, while normals and head-injured patients had normal serial position curves. During delayed recall, normals and head-injured patients did better than the two malingering groups on middle and recency portions of the list. Findings suggest that the serial position effect during learning trials may be a useful pattern of performance to watch for when suspicious of malingering.

The serial position effect in list-learning tasks is a well-established finding. In those with normal memory, items at the beginning and end of a word list are recalled better than items in the middle. The better recall of items at the beginning of a word list is called the primacy effect and the better recall of items at the end of a word list is called the recency effect. Together, the primacy and recency effects create a U-shaped performance curve on list recall tasks, which is seen in healthy individuals of all ages Carlesimo et al., 1997, Craik, 1970 and Rundus, 1971. Rundus (1971), who was among the first to explore this effect, suggested that the primacy effect occurs because words at the beginning of the list get more rehearsal and are, thus, consolidated into long-term memory, while the recency effect occurs because the words at the end of the list are still being held in short-term memory. Although this explanation is subject to debate, evidence from clinical populations is more or less supportive of the idea that the primacy and recency effects represent different and dissociable memory processes. For example, patients with Alzheimer's dementia, Huntington's dementia, and patients with severe amnesia secondary to Korsakoff's or bilateral media temporal lobe resection tend to show impaired primacy, with normal recency Baddeley & Warrington, 1970, Bigler et al., 1989, Burkart et al., 1998, Carlesimo et al., 1995, Gibson, 1981 and Massman et al., 1993 (though note lack of impaired primacy in amnesics in Carlesimo et al., 1995 and Hermann et al., 1996). However, studies suggest that closed head injury of varying severity does not affect the primacy effect Bernard, 1991, Bigler et al., 1989 and Suhr et al., 1997, though at least one study found that patients with closed head injury have an impaired recency effect, suggestive of attention/short-term memory difficulties (Bernard, 1991). A few studies have examined the use of the serial position curve in the detection of malingering. Bernard (1991) compared the Auditory Verbal Learning Test (AVLT) performance of undergraduate students asked to malinger head injury to patients with acute severe closed head injury and to healthy controls. Neither the malingering students nor the closed head-injured groups showed a normal serial position curve. However, the malingerers were impaired on the first third of the list (primacy effect), while the closed head-injured patients were impaired on the last third (recency effect). In a second study (Bernard, Houston, & Natoli, 1993), malingering undergraduates showed a normal U-shaped curve (there was no head-injured comparison group). Suhr et al. (1997) used the same method to assess the serial position curve in multiple patient groups, including (1) head-injured patients who were a priori defined as probable malingerers, (2) mild head-injured patients who were in litigation but did not meet a priori criteria for malingering, (3) mildly to moderately head-injured patients not in any litigation, (4) severely head-injured patients not in any litigation, and (5) psychiatric patients without history of head injury (somatization, depression). Results showed that all groups except those identified as probable malingerers showed the normal serial position curve. The malingering group had suppressed performance on the first third of the list and the middle part of the list. Thus, consistent with Bernard, the malingering pattern involved a suppressed primacy effect. The differences in findings on the recency effect with head-injured patients may be because head-injured patients in the Suhr et al. study were not in the acute stages of recovery and most were not as severely impaired. However, closed head-injured patients in both samples showed a normal primacy effect. Thus, the few studies assessing the effects of malingering on serial position suggest that malingerers suppress the primacy effect, a pattern not seen in closed head injury, though one that does inconsistently appear in other neurological disorders, particularly severe amnesia. The present study sought to replicate this finding and further test its specificity to malingering. The present study also examined whether the serial position pattern seen in malingerers is robust to coaching. Some research suggests that sophisticated malingerers, who are either coached about how to malinger on tests or about specific symptoms seen in head injury, may perform differently than naive malingerers on malingering and other neuropsychological tests Martin et al., 1993, Martin et al., 1992, Rose et al., 1998 and Youngjohn et al., 1999, although there is some evidence that some neuropsychological tests, or patterns of performance on such tests, may be more robust to sophisticated malingering Martin et al., 1996 and Suhr & Gunstad, 2000. A final goal of the present study was to explore the effects of malingering on the serial position effect in delayed recall. Early research established that, even when the primacy and recency effects are seen in learning or immediate recall, after a delay, the recall and recognition of primacy words is still superior to the middle words, while recency words are no longer better recalled Baddeley & Warrington, 1970, Craik, 1970 and Rundus et al., 1970. However, there may be differences in the pattern of primacy and recency in recall, based on age or neurological impairment. For example, Carlesimo et al. (1997) demonstrated that both young individuals (ages 20–35) and older persons (ages 60–80) showed the characteristic drop in recency items during delayed recall, the memory loss in the recency items was greater for the older group than for the younger. Massman et al. (1993) demonstrated that patients with Alzheimer's disease showed impaired primacy and recency during delayed recall of the CVLT, while patients with Huntington's disease showed only impaired recency. In another study (Carlesimo et al., 1995), patients with Alzheimer's disease showed only impaired recency, consistent with healthy controls, while patients with amnesia showed impairments in both primacy and recency. The present study examined the serial position curve over the learning trials and the delayed recall on the AVLT in three groups: normal controls, simulators, and head-injured patients similar in age and education. The goals were: (1) to examine the stability of malingering findings of differences in serial position curve and their specificity to malingering relative to closed head injury, (2) to see whether the malingering findings are robust (i.e., can withstand the effects of general coaching), and (3) to explore the differences in delayed serial position effect in head injury and malingering. It was hypothesized that malingerers would show less primacy effect than healthy controls or head-injured patients, and that this pattern would be seen regardless of coaching.