To survive in a complex changing environment humans frequently need to adapt their behaviour incidentally from normal interactions in the environment without any specific intention to learn. Whilst there is a considerable body of research into incidental learning of sequential information there is still fundamental debate regarding its cognitive basis, the associated neural mechanisms and the way in which it is affected by neurological disease. These issues were explored, in normal participants and neurological patients, using manipulations of the Serial Reaction Task [SRT] in which participants gradually learn a stimulus sequence (usually screen locations) after responding to each item by pressing corresponding response buttons. The first two experiments (chapter 3) demonstrate that the specific metric used to quantify learning and the occurrence of highly salient repeat locations may inflate estimates of learning in tasks with increased motor demands. The next three experiments (chapter 4) examine whether a secondary (not directly behaviourally relevant) information source during the SRT facilitates chunking in memory and overall learning. In a spatial SRT task (specified by horizontal location), additional spatial information (vertical location) enhanced learning but a secondary perceptual property (colour) produced a cost. However, in a perceptual SRT a secondary perceptual property (colour) had no effect. The next study demonstrates that impairments of incidental learning in Parkinson’s disease are partially reduced by administration of l-Dopa. Implications for models of striatal function and studies suggesting implicit learning is impaired by l-Dopa are discussed. Finally, the impact of Deep Brain Stimulation of the GPi is investigated in a population known to have only limited cognitive deficits relating to their illness (dystonia). Despite previous reports of impaired intentional learning in participants with a high genetic risk of Dystonia, there was no evidence for any impairment before or after stimulation. Implications across studies and future research directions are also discussed.

Next to practice itself, feedback provided to a learner from an external source such as a coach or therapist is considered the most important factor facilitating skill acquisition. Past research has suggested that punishment and reward feedback have dissociable effects on learning and retention, respectively. However, other studies have suggested a more reliable effect of punishment feedback while failing to replicate the benefit of reward on retention. This discrepancy across experiments may be the result of seemingly innocuous methodological differences. Here, I ran a pre-registered online experiment to test the replicability of the supposed dissociable effects of punishment and reward on learning during training and retention, respectively. Participants were randomly assigned to receive either punishment feedback (n = 34) or reward feedback (n = 34) during the training period as they learned a repeating 12-element sequence in a serial reaction time task. Feedback consisted of participants either seeing a red (Punishment group) or green (Reward group) box flash on their computer screen and, unbeknownst to them, either a corresponding loss (Punishment group) or gain (Reward group) of points from their starting total. Participants were informed that a good final point score (i.e., the higher the better) could earn them extra entries into a gift card lottery. Contrary to what much of the literature has found, our results revealed no statistically significant differences between groups in either the training or retention phases of the experiment. In conclusion, the findings of this experiment failed to replicate the previously found dissociable effects of punishment and reward feedback on learning and retention, respectively. The data instead suggests that providing participants with punishment or reward feedback may affect learning and retention in a similar manner. / Thesis / Master of Science (MSc) / The information that you get from your senses, along with the comments and criticisms given to you by others, are all forms of feedback that may or may not be available in your environment. Feedback can often be given to you in the form of a punishment or a reward in an effort to facilitate your performance of a motor skill, such as learning to juggle a soccer ball. In this thesis, I explored whether punishment and reward feedback have dissociable effects on the way people learn and retain a new motor skill. Some individuals received punishment feedback by seeing a red box flash on their screen and losing points, while others received reward feedback by seeing a green box flash on their screen and gaining points. Although the participants learned the new motor skill in the experiment, the results showed that reward and punishment feedback did not differentially impact motor learning. These results suggest that either reward or punishment feedback may be a useful feedback strategy for promoting motor learning.

This thesis aims to investigate how well associative learning can account for human sequence learning under incidental conditions. It seems that we can learn complex sequential information about events in our environment, for example language or music, incidentally, without being aware of it. Awareness is, however, a complex issue with arguments for (Dienes, 2012) and against (Shanks, 2005) the existence of implicit learning processes. A dual process account proposes that there exist two different learning systems, one based on conscious, controlled reasoning and rules, and the other based on automatic association formation, which can take place outside of awareness (McLaren, Green, & Mackintosh, 1994). This thesis attempts to use the predictions of an associative account in conjunction with a suitable method for investigating implicit learning: sequence learning (Destrebecqz & Cleeremans, 2003). The research involves a collection of serial reaction time (SRT) tasks whereby participants respond to on-screen stimuli that follow a sequence that they were (intentional learning) or were not (incidental learning) informed of. Following on from the experimental design of Jones and McLaren (2009) this thesis provides evidence that humans differ in their ability to learn different sequential contingencies. After training sequences of trials where the current trial location was twice as likely to be either: the same as (Same rule); or different to (Different rule) the location two trials before this, participants were far better at learning the latter rule. I found that this result was not adequately simulated by the benchmark associative model of sequence learning, the Augmented SRN (Cleeremans & McClelland, 1991), and present a revised model. This model, amongst other attributes, represents all the stimuli experienced by participants and can therefore learn stimulus-response contingencies. These seem to block learning (to some extent) about the Same rule thus providing an associative explanation of the advantage for acquisition of the Different rule. Further predictions regarding the role of additional stimuli alongside sequence learning were then derived from this associative account and tested on human participants. The first of these was that additional stimuli within the task will interact with sequence learning. I found that human participants show increased Same rule learning when additional, concurrently presented stimuli follow the previous element in the sequence. I demonstrate that when participants perform an SRT task where responses are predicted by the colour of a cue, they are able to learn about this relationship in the absence of awareness. Using this cue-response learning I further investigate cue-competition between sequences and colours under incidental conditions and find evidence that suggests between cue associations may alter the influence of cue competition. These results altogether suggest that stimuli – both simple and sequential – can be learned under incidental conditions. This thesis further proposes that learning about simple and more complex relationships between stimuli interacts according to the predictions of an associative account and provides evidence that contributes to a dual process understanding of human learning.

Procedural learning abilities have been shown to be deficient in children who meet criteria for Developmental Dyslexia (DD) and those who meet criteria for Specific Language Impairment (SLI; Lum et al., 2010; Menghini et al., 2006). Further, grammatical understanding has been linked to implicit sequence learning abilities across SLI and typically developing children (Lum, 2012). The present study examined implicit sequence learning, measured by the Serial Reaction Time Task (SRTT), in children who met criteria for DD with or without SLI. Implicit sequence learning was modeled using multi-level growth models of initial reaction time and learning slope across the repeated sequences of the SRTT. We further examined the predictive contributions of grammatical understanding, vocabulary abilities, phonological awareness, and diagnostic groups on implicit learning performance on the SRTT. Results showed language abilities and diagnostic group did not relate strongly to rates of implicit learning.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第22745号 / 医博第4663号 / 新制||医||1046(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 林 康紀, 教授 伊佐 正, 教授 村井 俊哉 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Punishment and reward feedback during motor learning tasks appear to have some beneficial impact on learning and retention, respectively. Therefore, it is possible that combining punishment and reward feedback would benefit both learning and retention. Within the sports coaching domain, a combination of punishment and reward feedback schedule has been suggested to improve performance. According to the coaching literature, the most effective approach is providing reward-to-punishment feedback. However, transitioning from punishment-to-reward feedback may be more effective based on the motor learning literature. The present study examined the utility of combining punishment and reward feedback through a transition schedule approach during a serial reaction time task. To test the competing predictions about feedback order, half the participants received punishment-to-reward feedback and the other half received the reverse order. Our results revealed that training response time significantly improved with no significant difference between the order of feedback. However, both types of feedback order did not improve retention during the same-day and delayed post-tests. Yet, the non-significant equivalence test indicates that these findings remain inconclusive. Finally, within-subjects analysis of the punishment and reward conditions found that training significantly improved response time with no difference between them. In this case, the equivalence test was significant, revealing that the estimated effect was surprisingly small. Overall, the current study failed to find conclusive evidence that the order of a transition feedback schedule matters for learning and retention. However, the difference between punishment and reward conditions may be smaller than previously assumed by motor learning studies. / Thesis / Master of Science (MSc) / An important part of learning any skill is receiving information that helps us recognize mistakes and improve our performance, known as feedback. In fact, feedback presented as a punishment or reward has been shown to improve an individual's ability to learn and retain skills, respectively. Therefore, can combining punishment and reward feedback benefit both learning and retention? One way to deliver both types of feedback is using a transition schedule. Some have recommended that transitioning from punishment to reward feedback would be most effective, while others have suggested the reverse order. The current study examined whether the order of receiving punishment and reward feedback affected learning and retention. To test this, subjects either received punishment-to-reward feedback or reward-to-punishment feedback during a key-pressing task. Our results did not find conclusive evidence that the order mattered for learning and retention. Furthermore, the difference between punishment and reward feedback overall was smaller than previously thought. These findings highlight that more studies may need to be conducted to get a better understanding of whether the order of punishment and reward feedback can benefit both learning and retention.

Dyslexi är en form av läs- och skrivsvårighet som inte kan förklaras av t.ex. bristfällig undervisning, låg begåvning eller synproblem. Orsaken till dyslexi anses vanligen vara nedsatt förmåga av fonologiskt processande. Flera studier har dock visat att dyslexi även är förknippat med språkliga, kognitiva och motoriska svårigheter som inte kan förklaras av nedsatt förmåga av fonologiskt processande. Det procedurella minnessystemet engageras vid inlärning, processande och konsolidering av kognitiva och motoriska färdigheter. Enligt the procedural deficit hypothesis (PDH) orsakas de svårigheter förekommande vid dyslexi av en nedsättning i detta minnessystem. Forskningen inom området är inte entydig då det har rapporterats om både intakt och nedsatt procedurellt minne hos personer med dyslexi. Föreliggande studie var den första att undersöka procedurellt minne hos svenska universitetsstuderande med dyslexi. Syftet var att testa PDH med hjälp av alternating serial reaction time task (ASRT), samt att undersöka relationen mellan procedurellt minne, närmare bestämt implicit sekvensinlärning, och läsförmåga samt aspekter av språklig/fonologisk förmåga. I studien deltog totalt 37 universitetsstuderande, 11 med dyslexi och 26 utan dyslexi. Resultatet indikerade att förmågan till inlärning och konsolidering i det procedurella minnet inte skilde sig åt mellan grupperna. Resultatet ger således inte stöd åt PDH. Vidare kunde inga signifikanta korrelationer påvisas, vilket tyder på att det inte föreligger något samband mellan procedurellt minne och respektive läsförmåga, fonologisk medvetenhet och snabb benämning (rapid automatized naming, RAN). / Developmental dyslexia is characterized by reading and writing difficulties that do not derive from poor education, low intelligence or visual impairment. The disorder is commonly explained as a result of an underlying phonological deficit. However, studies have shown that dyslexia is also associated with linguistic, cognitive, and motor impairments that can not be explained by a specific phonological deficit. The procedural memory underlies learning, processing and consolidation of motor and cognitive skills. The procedural deficit hypothesis (PDH) suggests that an impairment of procedural memory is the underlying cause of developmental dyslexia. Previous research has yielded inconsistent results as studies have reported intact as well as impaired procedural memory in dyslexics. This study was the first to examine procedural memory in Swedish university students. The aim was to test the PDH, by using an alternating serial reaction time task (ASRT), and to examine the correlation between procedural memory and reading ability as well as aspects of linguistic/phonological ability. In this study there was a total of 37 university students, 11 dyslexics and 26 nondyslexics. The result showed learning and consolidation of the procedural memory in both groups and there was no significant difference between the groups. Thus, the results do not support the PDH. No significant correlations were found, which indicates that there is no association between procedural memory and reading ability, phonological awareness or rapid automatized naming (RAN).

Prever eventos ambientais, com base em memórias sobre regularidades passadas, é uma das funções fundamentais de sistemas nervosos complexos. Eventos ordenados serialmente ou sequências estruturadas de estímulos permitem extrair informação passível de descrição formal que define seu padrão serial. Esse padrão inclui informações temporais e espaciais que facultam prever os próximos eventos da sequência, possibilitando a preparação prévia do organismo para lidar com sua ocorrência. Não surpreende que animais, incluindo o ser humano, aprendam, de maneira relativamente rápida, sobre regras e estruturas de padrões sequenciais de estímulos. O uso de tarefas de tempo de reação serial (TRS) é recorrente em estudos envolvendo a formação de associações, antecipação, atenção, as bases da memória e aprendizagem de relações complexas. Resumidamente, voluntários devem responder a estímulos apresentados em sequências repetitivas ou aleatórias. Com o treino, há redução no tempo de reação a cada estímulo, refletindo a aprendizagem de relações percepto-motoras. Essa redução, porém, é maior na sequência repetitiva em relação à sequência aleatória, indicando um aprendizado também sobre a sequência repetitiva, mesmo quando o voluntário não a percebe (conscientemente) e seja incapaz de relatar sua existência. Trata-se, portanto, de uma aquisição (inicialmente) implícita. A complexidade de uma sequência de estímulos pode ser expressa quantitativamente por meio de uma ferramenta matemática proposta por Shannon (1948), a entropia informacional (EI), que considera, entre outras coisas, a probabilidade de ocorrência dos estímulos em diferentes níveis. No presente trabalho, avaliamos em que extensão o conceito de EI permite prever o desempenho de ratos na tarefa de TRS envolvendo sequências com diferentes níveis de complexidade. Ratos foram treinados a reagir (1) a uma sequência repetitiva de estímulos, cuja quantidade de EI no nível 1 (que relaciona os estímulos da sequência 2 a 2) era 2,75. Após atingirem um nível assintótico de desempenho, os animais foram expostos (2) a sequências variáveis de estímulos com a mesma quantidade de EI no nível 1, porém, com maior quantidade de EI no nível 2 (que relaciona os estímulos da sequência 3 a 3). Numa etapa posterior os animais foram expostos (3) a uma nova sequência repetitiva de estímulos, cuja quantidade de EI no nível 1 era 3,00; por fim, os animais foram submetidos (4) a sequências variáveis com a mesma quantidade de EI no nível 1em relação à sequência anterior, porém, com maior quantidade de EI no nível 2 . Os resultados mostraram que os ratos aprenderam sobre os padrões seriais e, mais interessante, que seu desempenho esteve fortemente correlacionado à quantidade de EI no nível 2. Em outras palavras, quanto maior a EI, pior o desempenho dos animais tanto em termos do tempo de reação como em termos da percentagem de respostas corretas. Portanto, o conceito de EI permite não apenas quantificar a complexidade de sequências empregadas em estudos envolvendo aprendizagem serial, mas também prever o desempenho dos animais. / Prediction of environmental events, relying on memories of past regularities, is one of the fundamental functions of complex nervous systems. Sequences of serially ordered stimuli allow extracting information that defines its serial pattern. These patterns allow prediction of the next item in a sequence of events, facultating previous preparation to deal with its occurrence. Not surprisingly, animals, including humans, can identify rules present in serial structures of stimuli. Serial reaction time tasks (SRTT) have been extensively used in studies involving association, anticipation, attention, and learning and memory. Typically, subjects have to react to stimuli presented either in random or in repetitive sequences. As training proceeds, reaction time to each stimulus decreases, reflecting acquisition of this perceptual-motor skill. However, reaction time reduction is greater for repetitive sequences relative to the random sequences, indicating acquisition about the repetitive structure of the sequence. In human beings, this may occur even when the subject in uncapable of reporting the existence of a sequence, indicating that the acquisition was (at least initially) implicit rather than explicit. The complexity of a sequence of stimuli, at different levels, may be quantifyed by means of a mathematical tool proposed by Shannon (1948), the information entropy (IE). In this study we evaluated to which extent IE can predict performance of rats in SRTT involving sequences of stimuli organized at different levels of complexity. Rats were trained to react (1) a repeated sequence of stimuli which IE at the level \"1\" (i.e., expressing to which extent a given item allow prediction of the next) was 2.75. After reaching an asymptotic level of performance, the animals were exposed (2) a variable sequence of stimuli with the same amount of IE in the level \"1\", but with more IE in the level \"2\" (i.e., expressing to which extent two given items allow prediction of the next). Later the animals were exposed to (3) a new repeated sequence of stimuli, which IE at the level \"1\" was 3.00. Finally, the animals were submitted to (4) a random sequence of stimuli with the same amount of IE at the level \"1\", i.e., 3.00, but with greater IE in level 2. Results showed that rats learned about the serial patterns and, more interestingly, their performance strongly correlated to the amount of IE at the level \"2 \", both in terms of reaction times and in terms of percentage of correct responses. Therefore, IE allows not only to quantify complexity of sequences in studies involving serial learning, but also to predict performance of the subjects.

Experiências armazenadas acerca de regularidades passadas permitem a previsão do ambiente e, consequentemente, a possibilidade de ações antecipadas. Esta capacidade cognitiva é expressa em modelos de aprendizagem de sequências, que são capazes de acessar a previsibilidade das sequências de eventos e gerar descrições do desempenho em protocolos experimentais como a tarefa de tempo de reação serial. Nos experimentos 1, 2 e 3 deste trabalho, a abordagem informacional foi aplicada à descrição do desempenho na tarefa de tempo de reação serial. A relação entre medidas de entropia e desempenho na tarefa de tempo de reação serial envolvendo diferentes tipos de sequência foi investigada nos Experimentos 1a e 1b. As medidas de entropia foram feitas pelo processamento das frequências de eventos das sequências (i.e., pares, trios, quadras etc). Os resultados revelaram que a entropia informacional das sequências é um bom descritor do desempenho: (1) sequências de baixa entropia são realizadas mais rapidamente e são mais frequentemente reconhecidas ao final da sessão do que as de alta entropia; (2) uma curva sigmóide relaciona valores de entropia aos de tempo de reação: parâmetros \"min\" (tempo de reação com a previsão total), \"max\" (tempo de reação sem previsão) e \"x50\" (valor de entropia relacionada ao limiar de previsão); (3) o treinamento torna previsíveis sequências de alta entropia (o \"x50\" aumenta com o treinamento); e (4) com o treinamento, mais elementos prévios da sequência passam a ser utilizados para a previsão do próximo elemento. A relação entre desempenho e expectativas probabilísticas geradas durante o treinamento foi investigada no Experimento 2. Esse experimento envolveu múltiplas combinações de sequências de treino e teste, aplicadas a voluntários em sessões únicas. A diferença entre as previsibilidades das sequências de teste e treino foi quantificada pela distância de Kullback-Leibler: pequenas distâncias indicam que o treino proporciona boa previsão sobre o teste. Desconsiderando os efeitos de entropia (descrito no Experimento 1), a distância de Kullback-Leibler entre as sequências de teste e treino está relacionada ao desempenho: (1) distâncias pequenas levam à manutenção das expectativas (prévias) e tempos de reação curtos; (2) distâncias grandes levam à negligência das previsões e tempos de reação intermediários; e (3) distâncias intermediárias estão relacionadas a um conflito entre as estratégias de manutenção e negligência das expectativas, e geram tempos de reação elevados. Portanto, a flexibilidade das previsões ocorre em distâncias pequenas; uma estratégia alternativa, de negligência das previsões, é adotada em distâncias grandes. A estratégia desenvolvida nos Experimentos 1a e 1b foi útil para avaliar, no Experimento 3, a equivalência funcional entre treinamento imaginativo e real na aprendizagem de sequências. Este experimento envolveu voluntários testados na tarefa de tempo de reação serial ao longo de várias sessões de treinamento imaginativo e real. Os desempenhos durante o treinamento imaginativo e real foram descritos e comparados; o experimento mostrou também que a previsibilidade da sequência acessada por meio do treinamento imaginativo pode ser expressa posteriormente no desempenho real da tarefa. No entanto, o limite de previsibilidade das sequências acessado pelo treinamento imaginativo é inferior ao limite acessado por treinamento real, descrita pelo menor \"x50\" do (1) treinamento imaginativo em relação ao treinamento real e (2) desempenho real após o treinamento imaginativo em relação ao desempenho real após o treinamento real. Em conclusão, é possível afirmar que o modelo de entropia informacional é capaz de descrever a variabilidade do desempenho na tarefa de tempo de reação serial. Estes achados apóiam a existência de um princípio geral de acesso à previsibilidade para explicação da aprendizagem e memória. / Stored experiences of past regularities allow the prediction of the environment and, consequently, the possibility of anticipatory actions. This cognitive capacity is expressed in models of sequence learning, which are able to access the predictability of sequences of events and to generate descriptions of performance on experimental protocols as serial reaction time task. In Experiments 1, 2 and 3 of this work the informational framework was applied to the description of performance in serial reaction time task. The relationship between entropy measures and performance on serial reaction time task involving multiple sequence types was investigated on Experiments 1a and 1b. The entropy measures were done by processing the frequencies of events of the sequences (i.e. pairs, triads, quads etc). The results revealed that information entropy of the sequences is an impressively good descriptor of performance: (1) low entropy sequences were performed more rapidly and were more frequently recognized in the end of the session than the high entropy ones; (2) a sigmoid curve relates entropy to reaction time: parameters \"min\" (reaction time with total prediction), \"max\" (reaction time with no prediction) and \"x50\" (entropy value related to threshold of prediction); (3) training makes high entropy sequences predictable (the \"x50\" increases with training); and (4) with training, more previous elements of sequence are used for prediction of the next one. The relationship between performance and probabilistic expectancies generated during training was investigated on Experiment 2. This experiment involved multiple arrangements of training and testing sequences, applied to volunteers on single sessions. The difference between the predictabilities of testing and training sequences was quantified by the Kullback-Leibler divergence: small divergence indicates that training provides good prediction on testing. Disregarding the entropy effects (described on Experiment 1), Kullback-Leibler divergence between training and testing sequences is related to performance: (1) short divergences lead to (previous) predictions maintenance and low reaction times; (2) large divergences lead to predictions negligence and intermediate reaction times; and (3) intermediate divergences are related to conflict between the strategies of maintenance and negligence of predictions, and generate high reaction times. Therefore, the flexibility of predictions occurs on short divergences; an alternative strategy, of predictions negligence, is adopted on large divergences. The strategy developed on Experiments 1a and 1b was useful to evaluate, on Experiment 3, the functional equivalence between imagery and actual training on sequence learning. This experiment involved volunteers tested on serial reaction time task along multiple imagery and actual training sessions. Performances on both imagery and actual training were described and compared; the experiment also showed that the sequence predictability accessed on imagery training can be expressed on posterior actual performance. However, the limit of sequence predictability accessed by imagery training is lower than the limit accessed by actual training, described by the lower \"x50\" of (1) imagery training compared to actual training and (2) actual performance after imagery training compared to actual performance after actual training. In conclusion, it is possible to state that the entropy model is able to describe the variability of performance on serial reaction time task. These findings support the existence of a general principle of accessing the predictability to explain learning and memory.

This thesis consisted of experiments designed to explore the construct of attention and investigate the disruptive effects of psychotomimetics, with a specific focus on NMDA antagonists. Phencyclidine (PCP) was administered through a variety of treatment regimens in order to to determine the ability of inducing cognitive-specific disruptions in attentional functioning. The hypothesis that sub-chronic exposure to PCP would result in persistent attentional impairment was tested, using the 5-choice serial reaction time task (5-CSRTT). The 5-CSRTT assesses not only visuospatial attention, but also components of impulsivity, compulsivity, speed of processing and motivation. It was determined that an additional task-related intervention that increased the attentional load was required to elucidate attentional impairment following sub-chronic PCP treatment. The ability of rats to perform the modified version of the 5-CSRTT, known as the 5-choice continuous performance test (5C-CPT), was investigated. The 5C-CPT was implemented to provide a task that may have greater analogy to the human CPT, than the original 5-CSRTT. The consequence of dopaminergic D1 system activation was investigated. It was revealed that D1 partial agonism improved attentional performance in a baseline-dependent manner. Following successful acquisition of the task, it was shown that repeated PCP treatment induced cognitive disruption that was cognitive-specific, and not confounded by generalised response disruption. Furthermore, a partial attenuation of the PCP-induced performance disruption was achieved following administration of the D1 partial agonist, SKF 38393. Moreover, sub-chronic PCP treatment was shown to impair 5C-CPT performance in the drug-free state. However, an additional challenge that further increased the attentional load was needed to elucidate a performance deficit. This highlighted that sustained attention/vigilance is sensitive to persistent impairment following sub-chronic PCP administration in a manner consistent with deficits observed in schizophrenia patients. This prompted the investigation that tested the hypothesis that sub-chronic PCP treatment could induce enduring structural deficits in regions associated with attentional performance. Magnetic resonance imaging (MRI) was conducted, in conjunction with 5-CSRTT and pre-pulse inhibition (PPI). It was revealed that sub-chronic PCP treatment resulted in morphological brain abnormalities in brain regions associated with 5-CSRTT performance. This was coupled with deficits in sustained attentional performance following an increase in attentional load, yet PPI was unaffected. Taken together, these findings suggested sub-chronic PCP treatment impairs attentional functionality, an effect that dissociates between effortful and passive attentional processes.