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Research Article                                                                                                                                                       Open Access

## Recognition Memory for High and Low Associative Stimuli in Autistic Individuals with Outstanding Memory Skill

Nicola Neumann 1,2 , Christoph Braun 1 , Anna M. Dubischar-Krivec 1 , Sven Bölte 3

1 Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany 2 Center for Diagnostic Radiology and Neuroradiology, Functional Imaging Unit, University of Greifswald, Greifswald, Germany 3 Department of Women's and Children's Health, Karolinska Institutet Center of Neurodevelopmental Disorders (KIND), Karolinska Institutet, Stockholm, Sweden

Corresponding Author:

nicola.neumann@uni-greifswald.de

## Abstract

Background: Individuals  with  autism  exhibit  typical  recognition  memory  performance,  but they  show a reduced use of context and relational processing in more complex memory tasks. It is unclear whether the same is true for autistic individuals with exceptional memory skill for whom superior rote memory skill has been assumed.

Objective: In this study, we investigated recognition memory for high and low associative stimuli in autistic memory experts. In accord with the rote memory notion, we expected an equal recognition performance for high and low associative stimuli and superior memorizing of nonsense material compared to control participants.

Methods :  Seven  autistic  memory  experts  and  seven  typically  developed  control  subjects,  matched  according  to  age,  sex, handedness, and full-scale intelligence quotient (IQ), were examined on a continuous old-new recognition paradigm, including high or low associative pseudowords and shapes. Memory expertise was characterized as a currently present outstanding memory skill above the subject's general level of ability and above the general population and was validated through direct clinical observation or some form of credible evidence.

Results: Our  hypotheses  were  partially  corroborated  with  autistic  memory  experts  recognizing  high  and  low  associative shapes equally well in contrast to control participants who showed superior recognition of high associative shapes. However, memory experts did not outperform control participants in the recognition of low associative shapes. There were no differences for the recognition of pseudowords.

Conclusions: Findings do not indicate enhanced memory for nonsense material, but a failure to make use of semantic features of abstract stimuli as assumed for autism as a whole.

Key Words : Autism; memory; old/new paradigm; recognition; savant syndrome

## Introduction

In  the  domain  of  memory  function,  autism  is coined  by  diminished  non-cued  free  recall,  but largely  intact  priming,  cued  recall,  and  recognition (1;2). Furthermore, it has been argued that persons with  autism  do  not  apply  semantic  and  syntactic meaning for remembering (3;4). Nevertheless, more recent  framework  provides  good  reason  to  doubt such  an  approach  (5).  For  instance,  persons  with autism have been found to be sensitive to semantic associations (e.g., (6)), are capable of deep encoding, which  is  often  semantically  based  (e.g.,  (7)),  and show increased recognition by using semantic relationships  (8).  Ameli  and  colleagues  (9)  varied  the meaningfulness of visual stimuli and presented pictures  and  nonsense  shapes to  high-functioning  autistic individuals. They recognized more meaningful than nonsense material. On the other hand, under certain circumstances, individuals with autism spectrum  disorder  (ASD)  showed  a  diminished  use  of context  (10;11),  especially  on  memory  tests  that provide little support at retrieval (8).

However,  a  substantial  minority  of  the  persons with autism show some sort of outstanding skill in relation  to  their  general  intellectual  level  (12),  also labeled savant  skills. Due  to  changes  in  diagnostic practice in autism in the last 30 years, there may be prevalence  rates  of  savant  skills  including  exceptional cognitive skills up to 30% (13). For this subgroup,  some  sort  of  underlying  fundamentally  altered  memory  function  has  been  postulated.  A prominent account in this regard is rote memory (1416),  which  is  information  processing  that  avoids grasping  the  inner  complexities  and  inferences  of the subject that is being learned and instead focuses on memorizing the material mechanically, so that it can be recalled by the learner exactly the way it was read  or  heard.  Although  it  has  been  demonstrated that  autistic  savants  capture  a  structure  and  apply rules within their domain of expertise (such as music or calendar calculating; see (17)), nonmeaningful  memory  strategies  might  also  be  present, for example, in memory savants who are able to  remember  all  kinds  of  meaningless  information (18).

The  objective  of  the  present  study  was  to  compare  autistic  individuals  with  outstanding  memory and  typically  developed  control  persons  using  an old-new recognition memory paradigm of high and low associative pseudowords and shapes. In a previous study (19), we found that the same group of autistic individuals did not outperform control participants  in  the  recognition  of  pseudowords  or shapes. Thus, in the current  study,  we  did  not  expect a better overall performance of autistic memory experts in our standard old-new paradigm. Instead,  we  hypothesized  an  interaction  of  condition (high/low associative) and group in a way that control participants  show  a  memory  advantage  for high but not low associative stimuli. For the group of  autistic  memory  experts  we  expected  an  equal recognition  performance  on  low  and  high  associative material and, in addition, a better recognition of low  associative  stimuli  compared  to  control  subjects.

## Methods

Participants

As described in detail in Neumann et al. 2010 (19), eleven autistic individuals were recruited in cooperation with the Department of Child and Adolescent Psychiatry  and  Psychotherapy  of  the  Goethe  University  at  Frankfurt/M. They were selected from a larger  sample  for  a  magnet-encephalography study about autistic  memory savants  (19).  Four  were  ex- cluded because of an inability to follow the instructions or quit the experiment because of fatigue. All individuals  exhibited  idiopathic  autism  with  fluent speech and a nonverbal IQ >85. The clinical ICD10 diagnosis of autism (F84.0) was corroborated by assessments using the German forms of the Autism Diagnostic  Interview-Revised  (ADI-R,  20;21)  and the Autism Diagnostic Observation Schedule (22;23).

Based  on  parental  interviews  followed  by  direct clinical behavior observation, all autistic individuals were  classified  as  displaying  outstanding  memory skill. Thereby the scale for special, outstanding abilities  of  the  ADI-R  ('Interests  and  behaviors')  was used to define special memory abilities and to classify  memory  savants  if  they  were  currently  showing some outstanding memory skills above the subject's general level of ability and above the general population. Additionally, special abilities reported by parents were validated through direct clinical observation (demonstration of skill) or some form of credible evidence (e.g., school report). Exclusion criteria were anticonvulsive medication, an epileptic seizure less  than  2  years  prior  to  the  study,  and  additional severe  comorbid psychiatric  or  neurological  conditions, as assessed by reviewing information from the subject's medical file. Autistic memory experts were all male and right-handed, with a mean age of 21.4 years (range: 8-37; SD = 10.7) and a mean full-scale IQ  of  118  (range:  100-130;  SD  =  10.1).  Their  respective outstanding skills are described in Table 1. Seven typically developed individuals were recruited by summons at the University of Tübingen or were personally acquainted with the experimenters. They were matched according to sex, handedness, age (M = 20.3;  range:  8-36;  SD  =  10.3),  and  full-scale  IQ (M = 115; range: 100-124; SD = 9.6). General IQ was assessed with the Standard Progressive Matrices (24) in five of seven memory experts and all control participants.  In  two  of  seven  autistic  participants, general IQ had been assessed before with the German  versions  of  the  Wechsler  Adult  Intelligence Scale-Revised (25) or the Wechsler  Intelligence Scale  for  Children-Revised  (26).  Here,  intelligence was not tested a second time in order to save time because, in individuals with high-functioning ASD, performance on the Standard Progressive Matrices and Wechsler IQ tests are comparable (27). Scores of verbal IQ or scores of the Peabody Picture Vocabulary Test-III (PPVT-III) were only available for five  of  seven  autistic  memory  experts  (between  94 and 126, M = 109.8, SD = 13.6). Because of time constraints, scores of verbal IQ were not collected in the control group; however, due to the good verbal abilities of the autistic group, groups' means are not likely to differ.

TABLE 1. Characterization of autistic memory experts

| Memory Savant   |   Age | General IQ   | Verbal IQ   | Diagnosis           | Special Abilities                                                                                               |
|-----------------|-------|--------------|-------------|---------------------|-----------------------------------------------------------------------------------------------------------------|
| S 1             |     8 | 120 1        | 94 5        | Autistic disorder   | Memory for timetables and dates; visual-spatial abilities                                                       |
| S 2             |    37 | 124 2        | 122 4       | Autistic disorder   | Memory for timetables of dif- ferent transportation means; musical talent, absolute pitch; calendar calculation |
| S 3             |    15 | 130 3        | 126 3       | Asperger's disorder | Memory for timetables; draw- ing abilities                                                                      |
| S 4             |    18 | 110 2        | --          | Autistic disorder   | Memory for underground net- work; calendar calculation                                                          |
| S 5             |    19 | 100 3        | --          | Autistic disorder   | Memory for timetables and dates; mental arithmetic                                                              |
| S 6             |    34 | 124 2        | 105 4       | Autistic disorder   | Memory for train schedules and highway network of Ger- many; memory for dates                                   |
| S 7             |    15 | 119 2        | 102 5       | Autistic disorder   | Memory for timetables and maps, radio towers; early read- ing; mental arithmetic                                |

1

Colored Progressive Matrices; 2 Standard Progressive Matrices; 3 HAWIK/HAWIK-R; 4 HAWIE-R; 5 PPVT-III

Typically developed individuals were paid 8 € per hour  for  their  participation.  Autistic  memory  experts were  reimbursed  for travel expenses and accommodations, and they received a non-monetary gift for their participation. Children were reinforced with  tokens  during  the  experiment  that  they  could exchange for a gift,  which had been chosen in accord  with  their  parents.  According  to  self-report, autistic  experts  were  highly  motivated  to  demonstrate  their  exceptional  skills.  All  participants,  or their legal agents, gave informed consent to participate  in  the  study  that  was  approved  by  the  Ethics Committee of the Medical Faculty of the University of Tübingen.

## Experimental procedure

Participants  were  tested  in  a  continuous  old-new paradigm (28;29). In a block, 300 stimuli were presented continuously every 2 seconds, 100 of which were  displayed  only  once  ('new'),  100  of  which were displayed for a second time ('old'), and 100 of which were displayed once, but excluded from further  analysis  (filler  items).  All  participants  were  instructed to judge, as quickly and accurately as possible  by  pressing  a  button  with  their  right  and  left hand, whether an item had been presented before. Left and right button presses for 'old' and 'new' responses  were  counterbalanced  across  subjects. Stimuli were taken from the 'Verbal and nonverbal learning test' (30;31; Figure 1). They comprised a block  of  300  pseudowords  and  a  block  of  300 shapes, half of which were high and half of which were  low  associative  according  to  the  test  manual. Stimuli  were  pseudo-randomized  with  regard  to their  semantic category (high/low associative) with no more than five of each category in a row. The order of presenting either the block of pseudowords or shapes first was counterbalanced across subjects. The  interval  between  the  presentation  of  an  item and  its  repetition  was  between  6  and  12,  with  a mean  of  9  items.  Using  a  self-written  DOS  program, stimuli were projected centrally on a translucent screen using a Pentium-S 133-MHz computer and  an  NEC  GT2150  projector.  Participants  were seated at a distance of 92 cm at a vertical visual angle  of  1.2  degrees  and  a  horizontal  visual  angle  of maximal 6.2 degrees. At the beginning of each session,  the  participants  were  instructed  and  started with a short practice block to ensure that they understood the task. The proper block started with a central  fixation  cross  for  1  s.  Then  the  stimulus (pseudo-word or shape) was presented for 500 ms, followed  by  the  answering  period  that  pseudorandomly  varied  between  1.4  and  2.2  s.  The  next trial started with the following stimulus.

TEUBED

Figure 1. Stimuli used in the study from: "Verbal and nonverbal

Figure 1. Stimuli used in the study from: 'Verbal and nonverbal learning test' (30,31). High (left) and low (right) associative pseudowords are presented in the upper row. High (left) and low (right) associative shapes are presented in the lower row

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## Data analysis

Performance  on  a  yes/no  recognition  test  can  be summarized  by  two  measures:  the  hit  rate  (the probability that the subject classifies an old item as old),  and  the  false  alarm  rate  (the  probability  that the participant classifies a new item as old). According  to  Snodgrass  and  Corwin  (32),  the  discrimination index Pr and the bias index Br derived from a two-high threshold  model  were  calculated  for  the memory  data.  Higher Pr values  p (hit)  p (false alarm)  indicate better discrimination  ability  between old and new items. Br  p (false alarm) / p (1  Pr )  represents the measure of response bias. Br values higher than 0.5 indicate liberal response criteria (tendency to respond 'old'); values lower than 0.5 suggest  conservative  response  criteria  (tendency  to respond  'new').  The  discrimination  index Pr and the  response  bias Br during  the  recognition  of pseudowords and shapes were analyzed using a repeated-measures analysis  of  variance  (ANOVA) with  the  within-factor  'condition'  (high  vs.  low associative) and the between-factor 'group' (memory experts vs. control participants). Reaction times were analyzed with a repeated-measures ANOVA with the within-factors 'condition' (high vs. low associative), 'response' (hits vs. false alarms),  and  the  between-factor  'group'  (autistic memory experts vs. control participants).

## Results

Pseudowords

Discrimination index Pr:

For means and standard deviations of hit and false alarm rates in the recognition of high and low associative pseudowords, refer to Table 2. The repeatedmeasures  ANOVA  revealed  no  main  effects  of condition  (F1,12  =  0.11, P =  .75  ,  p 2   =  0.01),  or group (F1,12 = 2.43, P = .15,  p 2  = 0.17), or an interaction between condition and group (F1,12 = 0.003, P = .96,  p 2  < 0.001).

## Response bias Br:

The  repeated-measures  ANOVA  revealed  a  trend towards  a  main  effect  of  group  (F1,12  =  4.29, P = .06,  p 2  = 0.26) with autistic memory experts showing a conservative and control participants a liberal response bias. There was no main effect of condition (F1,12 = 1.01, P = .33,  p 2  = 0.08) nor an interaction between condition and group (F1,12 = 0.19, P = .67,  p 2  = 0.02).

TABLE 2 . Performance data (M = mean; SD = standard deviation) for autistic memory experts and control participants in the recognition of high and low associative pseudowords and shapes

|               | Performance   | Performance        | Memory Experts M(SD)   | Control Par- ticipants M(SD)   |
|---------------|---------------|--------------------|------------------------|--------------------------------|
| Pseudo- words | Hits          | High associative   | 0.58 (0.21)            | 0.81 (0.15)                    |
| Pseudo- words |               | Low associative    | 0.57 (0.17)            | 0.79 (0.15)                    |
| Pseudo- words | False alarms  | High associative   | 0.28 (0.17)            | 0.35 (0.16)                    |
| Pseudo- words |               | Low associative    | 0.26 (0.15)            | 0.32 (0.15)                    |
| Pseudo- words | Pr            | High associative   | 0.30 (0.20)            | 0.46 (0.18)                    |
| Pseudo- words |               | Low associative    | 0.31 (0.19)            | 0.47 (0.23)                    |
| Pseudo- words | Br            | High associa- tive | 0.40 (0.23)            | 0.65 (0.26)                    |
| Pseudo- words |               | Low associa- tive  | 0.38 (0.21)            | 0.62 (0.19)                    |
| Shapes        | Hits          | High associative   | 0.57 (0.17)            | 0.71 (0.25)                    |
| Shapes        |               | Low associative    | 0.67 (0.28)            | 0.67 (0.27)                    |
| Shapes        | False alarms  | High associative   | 0.31 (0.20)            | 0.16 (0.12)                    |
| Shapes        |               | Low associative    | 0.57 (0.26)            | 0.52 (0.30)                    |
| Shapes        | Pr            | High associative   | 0.26 (0.22)            | 0.55 (0.31)                    |
| Shapes        |               | Low associative    | 0.10 (0.07)            | 0.14 (0.07)                    |
| Shapes        | Br            | High associative   | 0.40 (0.20)            | 0.44 (0.30)                    |
| Shapes        |               | Low associative    | 0.64 (0.29)            | 0.60 (0.33)                    |

## Reaction times:

Means  and  standard  deviations  of  reaction  times during the recognition  of  high  and  low  associative pseudowords are depicted in Table 3. The repeatedmeasures ANOVA revealed an interaction between the  factors  response  and  group  (F1,12  =  8.07, P < .05,  p 2 = 0.40), with control persons reacting significantly  faster  in  hits  than  in  false  alarms  (F1,12  = 5.16, P <  0.05,  p 2   =  0.30).  There  was  a trend toward  faster  reaction  times  of  autistic  memory  experts in false alarms compared with control participants (F1,12 = 3.96, P = .07,  p 2  = 0.25).

TABLE 3. Reaction times (in milliseconds; M = mean; SD = standard deviation) of autistic memory experts and control participants in the recognition of high and low associative pseudowords and shapes

| Reaction Times   | Reaction Times   | Reaction Times                   | Memory Experts M(SD)   | Control Participants M(SD)   |
|------------------|------------------|----------------------------------|------------------------|------------------------------|
| Pseudo- words    | Hits             | High associative Low associative | 771 (211) 752 (236)    | 807 (103) 836 (142)          |
|                  | False            | High associative                 | 623 (153)              | 872 (160)                    |
|                  | alarms           | Low associative                  | 805 (387)              | 894 (183)                    |
| Shapes           | Hits             | High associative                 | 786 (265)              | 846 (183)                    |
|                  |                  | Low associative                  | 745 (335)              | 882 (123)                    |
|                  | False            | High associative                 | 791 (374)              | 864 (174)                    |
|                  | alarms           | Low associative                  | 670 (208)              | 848 (95)                     |

## Shapes

## Discrimination index Pr:

For means and standard deviations of hit and false alarm rates in the recognition of high and low associative  shapes,  refer  to  Table  2.  The  repeatedmeasures ANOVA revealed a main effect of condition (F1,12 = 16.0, P < .01,  p 2  = 0.57) with high associative  shapes  showing  a  higher  discrimination index  than  low  associative  shapes.  There  was  a trend toward a main effect of group (F1,12 = 4.35, P = .059,  p 2   =  0.27),  with  control  participants  outperforming autistic memory experts. There was also a  trend  toward  an  interaction  between  condition and group (F1,12 = 2.98, P = .055, one-tailed,  p 2  = 0.20).  Post-hoc t -tests  revealed  that  only  control participants showed a higher discrimination index in high than in low associative shapes (F1,12 = 16.2, P < .01,  p 2  = 0.58). There was a trend toward a higher discrimination index of control participants compared with autistic memory experts in high but not low associative shapes (F1,12 = 3.92, P = .07,  p 2   = 0.25).

## Response bias Br:

The  repeated-measures  ANOVA  revealed  a  main effect of condition (F1,12 = 9.15, P < .05,  p 2  = 0.43) with a more liberal response bias in low associative shapes. There were no effects of group (F1,12 < 0.01, P =  1.0,  p 2   <  0.001)  nor  an  interaction  between condition and group (F1,12 = 0.28, P <= .61,  p 2   = 0.02).

## Reaction times:

Means  and  standard  deviations  of  reaction  times during the recognition  of  high  and  low  associative shapes  are  depicted  in  Table  3.  The  repeatedmeasures  ANOVA revealed  a  trend  toward  an  interaction between condition and group (F1,12 = 2.58, P =  .07, one-tailed,  p 2 =  0.18), with autistic memory experts showing a trend toward faster responses to low associative compared to high associative shapes (F1,12 = 4.07, P = .067,  p 2  = 0.25).

## Discussion

We investigated seven autistic memory experts and seven control participants in a recognition memory paradigm  with  high  and  low  associative  pseudowords  and  shapes.  We  expected  an  interaction  of condition  and  group  with  control  participants  but not autistic memory experts showing a recognition advantage  for  high  associative  material.  This  hypothesis was  confirmed  for the recognition of shapes, in which control participants outperformed autistic  memory  experts  in  the  recognition  of  high but not low associative stimuli. Autistic memory experts showed similar discrimination indices for the recognition of high and low associative shapes and did not differ from the control group in the discrimination index of low associative shapes. The overall recognition performance was quite low, but hit rates exceeded false alarm rates in all conditions, so that random button press due to missing comprehension or motivation can be ruled out. For the recognition of pseudowords, neither of the groups scored better on high than on low associative pseudowords, and thus our study could not replicate the classification provided  by  the  'Verbal  and  nonverbal  learning test'  (30;31).  The  absence  of  this  effect  represents an unfortunate failure to capture the variable under study.  Interestingly,  regardless  of  the  associative value of pseudowords, the group of autistic memory experts  showed  a  comparable  discrimination  index to control participants.

How can these findings be interpreted with regard to memory mechanisms in a group of autistic individuals  with  outstanding  memory  skill?  First,  outstanding memory  skill in a circumscribed area seemed  not  to  have  transferred  to  a  recognition memory  paradigm  with  standard  stimuli.  Rather than being superior in the recognition of nonsense shapes, our group of autistic memory experts turned out to be inferior in the recognition of shapes with high associative  value.  On  the  other  hand,  in  contrast  to  Ameli  and  coworkers  (9),  whose  autistic sample performed overall worse than control participants in a visual recognition memory task and particularly bad on the recognition of nonsense shapes, our autistic sample showed at least comparable dis- crimination indices to control participants in pseudowords and low associative/nonsense shapes. Their memory expertise, as well as their higher level of  intelligence,  may  thus  have  contributed  to  their normative  performance.  Second,  autistic  memory experts recognized surprisingly few high associative shapes  in contrast to control participants,  who showed the highest discrimination index of all conditions. The autistic group thus did not benefit from the  high  associative  value  of  shapes  to  an  extent that the control group did. Previous studies that investigated  recognition  of  common  objects  (33)  or semantic priming with picture stimuli  (34)  demonstrated  the  intactness  or  superiority  of  non-savant autistic  individuals  compared  with  control    participants.  However,  one  study  using  a  false  memory paradigm with geometric figures (35) found that individuals with ASD were significantly better able to discriminate  true  items  from  lure  items  and  from that  inferred  restrictive  associative  networks  in  the spatial  domain.  In  another  study  (9),  individuals with  ASD showed clearly  inferior  recognition  performance of nonsense stimuli similar to the low associative ones of the current study, but recognition of  common objects comparable to  that  of  control participants.  Taken  together,  these  results  provide evidence for an unimpaired or even superior pictorial semantic memory for objects, but a difficulty in making use of semantic features of abstract stimuli to  facilitate  memory  in  a  self-organized  manner. This  interpretation  is  in  accord  with  findings  that revealed a deficiency in the use of verbal mediation strategies  to  maintain  and  monitor  goal-related  information  in  working  memory  of  autistic  children (36;37). Similarly, in verbal memory paradigms, autistic  individuals  were  able  to  use  semantic  information  to  facilitate  memory  (6),  but  they  showed diminished relational processing and may not do so spontaneously (5;8). Beversdorf and colleagues found a restricted use of semantic networks in individuals  with  ASD  using  false  memory  paradigms, which was assumed to be mediated by abnormalities in  hippocampal  functioning  (10;11).  Third,  as  our sample  of  autistic  individuals  was  endowed  with special memory skill, we expected a superior recognition of low-associative  stimuli.  Even  in  nonsavant  high-functioning  autistic  individuals,  the  intactness  or  superiority  of  visual-spatial  abilities  has often been demonstrated (38-40). According to the Theory  of  Enhanced  Perceptual  Functioning  (41) there is a generally enhanced processing of low-level perceptual information leading to advantages in, for example, block design and embedded figures tasks (42-44).  However, in  contrast  to  other  studies, the current  investigation  used  a  large  number  of  complex  stimuli  combined  with  short  exposure  times

(i.e., 500 ms). This experimental design may be disadvantageous for autistic memory experts to reveal

their mnemonic skills.

There  were  group  differences  in  reaction  times during  the  recognition  of  shapes,  when  autistic memory experts tended to react faster to low than to high associative stimuli. On the other hand, they had the highest false alarm and the lowest discrimination rate of all conditions. Their fast reaction can therefore not be attributed to good performance; it may rather reflect  a premature  reaction  to  difficult stimuli. Autistic persons sometimes exhibit inhibitory deficits, especially with increasing cognitive load (45).  In  this  context  it  was  surprising  that,  during the  recognition  of  pseudowords,  autistic  memory experts  showed a more conservative response bias than control participants, that is, a tendency to 'no' responses when unsure. In typically developing individuals,  a  false  recognition  (a  tendency  to  'yes' responses)  often  occurs  under  speeded  response conditions in the early stages of (automatic) recognition  (46).  On  the  other  hand,  a  more  conservative response  bias  has  also  been  observed  in  other  patients groups, such as individuals with schizophrenia (47) or persons under alcohol-induced memory impairment (48), and might accompany lower recognition performance.

A limiting factor  of  the  current  study  is  the  fact that  a  control  group  of  individuals  with  ASD  but without memory skill is missing. Therefore, we are not able to disentangle effects of autism and savant syndrome. Another drawback may be the small and inhomogeneous sample that includes autistic memory experts  of  different  ages  and  reduces  the statistical  power.  However,  since  the  savant  syndrome is a rare condition, we were not able to increase the sample size. With regard to the heterogeneity  of  special  memory  areas  (timetables,  dates, etc.),  we  chose  a  recognition  paradigm with  standard stimuli. This may have been disadvantageous for probing savant memory. In future studies, memory performance may be improved by choosing tests in which stimuli reflect the savant domain.

In sum, in accord with our hypotheses, the group of  individuals  with  ASD  and  special  memory  skill showed a comparable recognition performance for high and low associative shapes but was inferior in the recognition of high associative shapes compared with  control  participants.  Contrary  to  prediction, autistic memory experts did not outperform control participants  in  the  recognition  of  low  associative shapes.  Although  there  is  evidence  for  restrictive associative networks in the spatial (as well as verbal) domain in the autistic, non-savant population (35), we attribute these findings to a failure to make use of semantic features of abstract stimuli to facilitate memory, possibly by verbal mediation strategies.

## References

1. Bowler DM, Matthews NJ, Gardiner JM. Asperger's syndrome and memory:  similarity  to  autism  but  not  amnesia.  Neuropsychologia 1997;35(1):65-70.
2. Minshew  NJ,  Goldstein  G.  The  pattern  of  intact  and  impaired memory functions in autism. J Child Psychol Psychiatry  2001;42: 1095-1101.
3. Hermelin  B,  O'Connor  N.  Remembering  of  words  by  psychotic and subnormal children. Br J Psychol 1967;58(3):213-18.
4. O'Connor N, Hermelin B. Auditory and visual memory in autistic and normal children. J Ment Defic Res 1967;11:126-31.
5. Gaigg SB, Gardiner JM, Bowler DM. Free recall in autism spectrum  disorder:  the  role  of  relational  and  item-specific  encoding. Neuropsychologia 2008;46 (4):983-92.
6. Beversdorf DQ,  Anderson  JM,  Manning  SE, Anderson  SL, Nordgren RE, Felopulos GJ et al. The effect of semantic and emotional  context  on  written  recall  for  verbal  language  in  high  functioning adults with autism spectrum disorder. J Neurol Neurosurg Psychiatry 1998;65(5):685-92.
7. Mottron L, Morasse K, Belleville S. A study of memory functioning  in  individuals  with  autism.  J  Child  Psychol  Psychiatry  2001; 42(2):253-60.
8. Bowler DM, Gaigg SB, Gardiner JM. Effects of related and unrelated  context  on  recall  and  recognition  by  adults  with  highfunctioning autism spectrum disorder. Neuropsychologia 2008;46(4):993-99
9. Ameli R, Courchesne E, Lincoln A, Kaufman AS, Grillon C. Visual memory  processes  in  high-functioning  individuals  with  autism.  J Autism Dev Disord 1988;18(4):601-15.
10. Beversdorf  DQ,  Narayanan  A,  Hillier  A,  Hughes  JD.  Network model of decreased context utilization in autism spectrum disorder. J Autism Dev Disord 2007;37(6):1040-48.
11. Beversdorf  DQ,  Smith  BW,  Crucian  GP,  Anderson  JM,  Keillor JM, Barrett AM et al. Increased discrimination of "false memories" in autism spectrum disorder. Proc Natl Acad Sci USA 2000;97(15):8734-37.
12. Treffert DA. The savant syndrome: an extraordinary condition. A synopsis: past, present, future. Philos Trans R Soc Lond B Biol Sci 2009;364(1522):1351-57.
13. Howlin P, Goode S, Hutton J, Rutter M. Savant skills  in autism: psychometric approaches and parental reports. Philos Trans R Soc Lond B Biol Sci 2009; 364(1522):1359-67.
14. Bölte S, Poustka F. Comparing the intelligence profiles of savant and nonsavant individuals with autistic disorder. Intelligence 2004;32:121-31.
15. Hill AL. An investigation of calendar calculating by an idiot savant. Am J Psychiatry 1975;132(5):557-60.
16. Toichi M, Kamio Y. Long-term memory and levels-of-processing in autism. Neuropsychologia 2002;40(7):964-69.
17. Miller  LK.  The savant  syndrome: intellectual impairment and exceptional skill. Psychol Bull 1999;125(1):31-46.
18. Treffert DA (2006) Extraordinary people. iUniverse, Inc., Lincoln, NE
19. Neumann N, Dubischar-Krivec  A,  Braun  C,  Löw  A,  Poustka  F, Bölte S et al. The mind of the mnemonists: an MEG and neuropsychological  study  of  autistic  memory  savants.  Behav  Brain  Res 2010;215(1):114-21.
20. Bölte S, Rühl D, Schmötzer G, Poustka F. Diagnostisches Interview für Autismus - Revidiert (ADI-R). Huber, Bern; 2006.
21. Lord  C,  Rutter  M,  Le  Couteur  A.  Autism  Diagnostic  InterviewRevised: a revised version of a diagnostic interview for caregivers of  individuals  with  possible  pervasive  developmental  disorders.  J Autism Dev Disord 1994;24(5):659-85.
22. Lord  C,  Risi  S,  Lambrecht  L,  Cook  EH,  Jr.,  Leventhal  BL, DiLavore  PC  et  al.  The  autism  diagnostic  observation  schedulegeneric:  a  standard  measure  of  social and  communication deficits associated  with  the  spectrum  of  autism.  J  Autism  Dev  Disord 2000; 30(3):205-23.
23. Rühl  D,  Bölte  S,  Feineis-Matthews  S,  Poustka  F.  Diagnostische Beobachtungsskala  für  Autistische  Störungen  (ADOS).  Huber, Bern; 2004.
24. Raven JC. The comparative assessment of intellectual ability. Br J Psychol 1948;19:137-50.
25. Tewes U. HAWIE-R. Hamburg-Wechsler Intelligenztest für Erwachsene, (Revision 1991). Hans Huber, Bern; 1994.
26. Tewes  U.  HAWIK-  R.  Hamburg-  Wechsler-  Intelligenztest  für Kinder. (Revision 1983). Hans Huber, Bern; 1993.
27. Bölte S, Dziobek I, Poustka F. Brief Report: The Level and Nature of  Autistic  Intelligence  Revisited.  J  Autism  Dev  Disord  2009; 39:678-82.
28. Rugg MD, Allan K. Event-related potential studies of memory. In: Tulving  E,  Craik  FIM  (eds).  The  Oxford  handbook  of  memory. Oxford University Press, Oxford; 2000:521-37.
29. Sanquist TF, Rohrbaugh K, Syndulko K, Lindsey DB. Electrocortical  signs  of  levels  of  processing:  Perceptual  analysis and recognition memory. Psychophysiology 1980;17:568-76.
30. Sturm W, Willmes K. Verbaler Lerntest. Hogrefe Verlag, Göttingen; 1999.
31. Sturm  W,  Willmes  K.  Nonverbaler  Lerntest.  Hogrefe  Verlag, Göttingen; 1999.
32. Snodgrass  JG,  Corwin  J.  Pragmatics  of  measuring  recognition memory: applications to dementia and amnesia. J Exp Psychol Gen 1988;117(1):34-50.
33. Lopez B, Leekam SR. Do children with autism fail to process information  in  context?  J  Child  Psychol  Psychiatry  2003;44(2):285300.
34. Kamio Y, Toichi M. Dual access to semantics in autism: is pictorial access superior to verbal access? J Child Psychol  Psychiatry 2000;41(7):859-67.
35. Hillier A, Campbell H, Keillor J, Phillips N, Beversdorf DQ. Decreased  false  memory  for  visually  presented  shapes  and  symbols among adults on the autism spectrum. J Clin Exp Neuropsychol 2007;29 (6):610-16.
36. Joseph  RM,  Steele  SD,  Meyer  E,  Tager-Flusberg  H.  Self-ordered pointing in children with autism: failure to use verbal mediation in the  service  of  working  memory?  Neuropsychologia  2005;43(10): 1400-11.
37. Joseph RM, McGrath LM, Tager-Flusberg H. Executive dysfunction and its relation to language ability in verbal school-age children with autism. Dev Neuropsychol 2005;27(3):361-78.

38. Minshew NJ, Goldstein G, Siegel DJ. Neuropsychologic functioning  in  autism:  profile  of  a  complex  information  processing disorder. J Int Neuropsychol Soc 1997;3(4):303-16.
39. O'Riordan M, Plaisted K. Enhanced discrimination in autism. Q J Exp Psychol A 2001;54(4):961-79.
40. O'Riordan M A. Superior visual search in adults with autism. Autism 2004;8(3):229-48.
41. Mottron L, Dawson M, Soulieres I, Hubert B, Burack J. Enhanced perceptual functioning in autism: an update, and eight principles of autistic perception. J Autism Dev Disord 2006;36(1):27-43.
42. Jolliffe  T,  Baron-Cohen  S.  Are  people  with  autism  and  Asperger syndrome  faster  than  normal  on  the  Embedded  Figures  Test?  J Child Psychol Psychiatry 1997; 38(5):527-34.
43. Shah A, Frith U. An islet of ability in autistic children: a research note. J Child Psychol Psychiatry 1983;24(4):613-20.
44. Shah A, Frith U.  Why do autistic  individuals  show  superior  performance  on  the  block  design  task?  J  Child  Psychol  Psychiatry 1993;34(8):1351-64.
45. Rinehart NJ, Bradshaw JL, Tonge BJ, Brereton AV, Bellgrove MA. A neurobehavioral examination of individuals with highfunctioning autism and Asperger's disorder using a fronto-striatal model of dysfunction. Behav Cogn Neurosci Rev 2002;1(2):164-77.
46. Heit  E,  Brockdorff  N,  Lamberts  K.  Strategic  processes  in  false recognition memory. Psychon Bull Rev 2004;11(2):380-86.
47. Ragland JD, Moelter ST, McGrath C, Hill SK, Gur RE, Bilker WB et  al.  Levels-of-processing  effect  on  word  recognition  in  schizophrenia. Biol Psychiatry 2003;54(11):1154-61.
48. Mintzer MZ, Griffiths RR. Alcohol and false recognition: a doseeffect study. Psychopharmacology (Berl) 2001;159(1):51-57.

## Acknowledgments

This work was supported by the Graduate Research Training  Program  on  Cognitive  Neurobiology  of the  Deutsche  Forschungsgemeinschaft  (DFG)  at the  University  of  Tübingen,  the  University  and Science  Program  of  the  Federal  State  of  BadenWürttemberg, and the Käthe Kluth Program of the University of Greifswald. The authors thank all patients for their participation in this  study.  The authors declare that they have no conflict of interest.