Psychological methods and the study of cognitive functions

Cognitive neurosciencePsychological methods and the study of cognitive functionsSanja Šešok*, Jože Jensterle*** SPS Nevrološka klinika,Klinični center Ljubljanae-mail: sanja.sesok@uni-lj.si**Psihiatrična klinika LjubljanaStudenec 48, 1260 Ljubljana Poljee-mail: joze.jensterle@psih-klinika.siAbstractDue to rich historical legacy as well as recent advances in thefield, cognitive psychology spans a large array of researchmethods, experimental paradigms and measuring techniquesthat provide a powerful set of tools in the study of cognitivefunctions. A sample of research methods from two core approaches,experimental psychology and cognitive neuropsychology,are presented along with some of the examples andconsiderations of their use.IntroductionThrough the history of psychology, many research methods havebeen developed. The rise of cognitive paradigm has also broughtabout a development of many new and exciting research methods,experimental paradigms and measuring techniques. Todaywe can observe four general approaches to research in cognitivepsychology.One way of studying cognitive processes is by making useof introspection. Even though dependent on conscious experience,introspection can provide us with valuable insights intostudied phenomena. Many researches (Nisbett and Wilson, 1977;Seger, 1994; cit. in Eysenck, 1995) argue that an individual’sintrospections about what is determining his or her behaviourare often inaccurate and limited in scope due to lack of consciousawareness of many cognitive processes or their products.But even though sometimes despised as subjective and unscientific,introspection has again found its validity and place in psychology,especially when properly used and interpreted. Ratherthan told to interpret their experience participants are nowadaysasked to describe the contents of focal attention. Their reportsare not used as a direct description of cognitive processes, butrather treated as any other behavioral data 1 .Cognitive processes and structures can also be explored indirectlyby observing the behaviour to which they lead, like measuresof speed and accuracy of performance. This approach hasproved to be useful in the development and subsequent testingof the majority of theories in cognitive psychology. The problemwith use of such data is that they provide only indirect informationabout internal processes. Behavioural data are alsousually gathered in the laboratory setting, which can often differsubstantially from real-life situations. Despite their drawbacks,classical experimental methods still present the core approachto testing and developing models of cognitive functions.Ingenious experimental designs have provided many breakthroughsin understanding human cognition.With fast development of computers and computing techniques,computational modeling today presents a very useful1One of important introductions of introspection as a valid scientificmethod can be found in Dennett’s book “Consciousness Explained” (1991).approach in the study of cognitive functions. Building runningmodels of cognitive functions not only forces psychologists tospecify in detail every assumption and detail of a theory, butalso provide a powerful means for their testing and development.Another very popular way of studying cognitive processes,also brought about by recent development in technology, is themore direct approach of measuring actual brain functioning duringperformance of a cognitive tasks. New technical advancesenable researchers to measure activity in different parts of thebrain with high spatial and temporal resolution.As functional brain imaging techniques and computationalmodeling are presented in detail elsewhere in this volume, ourpresentation of methods and studies of cognitive function willmostly focus on two core psychological approaches: experimentalcognitive psychology and cognitive neuropsychology.Experimental cognitive psychologyTheoretical models in cognitive psychology characterize mindas a complex information-processing system. The aim of researchin cognitive psychology is to specify the functional processesand representations that underlie performance on cognitive tasks.Information-processing framework assumes specific propertiesof the cognitive system, like limited capacity and sequential operation,which enables it to put forward specific hypotheses aboutresponses, their reaction times and accuracy that can be testedin experimental settings.Chronometric methodsReaction times (RT) provide an intuitively appealing indirectmeasure of brain function and efficiency. The time-honored procedureof RT has many variations – simple, choice, disjuncitve,and associative, with regular or irregular foreperiod warning signals.For example, the “subtraction method” enables us to assesthe amount of time needed to complete a cognitive operation bycomputing the RT-difference between two tasks that differ onlyin the addition of the cognitive operation we are interested in.The most straight-forward application of the subtractionmethod involves comparison of two uncomplicated tasks, thesimple reaction time (SRT) task and the choice reaction time(CRT) task. In the SRT, subjects make a simple motor responseto a specified stimulus. The RT measures how long it takes thesubject to perceive the stimulus and execute the motor response.Choice RT tasks involve some additional degree of cognitiveprocessing and/or decision making as they demand a choiceamong at least two possible responses.In RT experiments timing parameters such as stimulus presentationduration and interstimulus interval frequently serve asadditional independent variables. Besides RT, response accu-19

Information society 2001racy can also be used as a dependent variable in a range of differentstimulus presentation paradigms with a number of taskperformance criteria. Combined with RT, it provides a measureof accuracy-speed tradeoffs, such as the changes in accuracywhen time to perform is changed. Finally, verbal reports by subjectsof their own conscious processes during task performancehave also been used as dependent measures in RT experiments.Sternberg’s paradigmThe basic paradigm for studying speed of retrieval from shorttermmemory was introduced into psychology by Sternberg(Eysenck, 1969). Sternberg built on the assumption that reactiontime from stimulus to response is really a composite or asum of reaction times of a series of sequential subprocesses thatone has to carry out in order to complete the task. He suggestedthat in order to study a specific component, one has to set up anexperimental task in which all other components are kept constantand only the component that we are interested in is systematicallyvaried. In his experiment, two to six items, generallyreferred to as the “memory set”, were presented to the subjectin short succession. A probe item was then presented shortlyafter the memory set. The subject’s task was to decide as rapidlyas possible whether or not the probe matched one of the items inthe memory set. The results showed that the reaction times increaselineary with number of items held in memory, which suggeststhat short-term memory scanning is a serial process.Tachistoscopic methodsTachistoscopic methods have proven to be extremely useful toolsfor addressing interesting questions in psychology and neuropsychology.Much of the early tachistoscopic research in psychologywas concerned with how much information a person couldapprehend from a single brief fixation and with the determinantsof visual “attention” (Hannay, 1986). The intensive applicationof tachistoscopic techniques to neuropsychological questions,especially to question of hemispheric asymmetries of function,is more recent, dating essentially from the 1960s. Standardizedand normed tachistoscopic tasks which provide information regardingthe nature and quality of hemispheric specializations,visual memory functions, simple visual sensory acuity and visualmotorresponse speed can be most useful in individual patientassessments.Dichotic listening researchThe dichotic listening task involves presenting subjects with twodifferent auditory stimuli simultaneously, one to each ear. Kimura(1961, cit. in Hannay, 1986) employed this procedure, using spokendigits as stimuli, with subjects known to have damage toeither the left or the right temporal lobe. Each trial consisted ofthree pairs of dichotic digits presented in rapid succession. Immediatelyafterwards, subjects were asked to recall as many ofthe six digits as possible, in any order. The main observationwas that even in neurologically normal subjects right ear advantage(REA) occurred. The participants typically reported itemspresented to the right ear with greater accuracy. On the basis ofevidence from animal studies Kimura explained that the earasymmetry is based on stronger contralateral than ipsilateralprojections from each ear.Vigilance tasksIn vigilance tasks, participants are typicaly presented with a specific task that has to be carried out over a longer period of time,aimed at assessing the participants’ ability to sustain their levelof performance. Several diferent types of vigilance tasks existthat differ in operations specified by stimulus presentation paradigmsand instructions to the subject.In monitoring, the subject is exposed to continuous stimulibut responds only to occasional signal or target items. Designedto keep memory, motor, learning and problem-solving requirementsto a minimum, while requiring continuous sustained attentionor “vigilance”, monitoring tasks are used to assess andaugument the subjects’ ability to maintain peak levels of alertnessand attention while performing monotonous tasks. Supervisorsin a production line or airspace controller often face suchsituations.Continuous performance task (CPT) is a relatively briefmeasure of vigilance. It was originally developed by Rosvoldand his associates (Hannay, 1986) and it is the most widely usedmeasure of sustained attention. CPT is a class of rapidly paced,relatively brief vigilance tasks with discrete target and nontargetperceptual stimuli, the exact nature and timing of which varysubstantially from one application to another. The CPT paradigmhas been much studied in cognitive electrophysiologywhere it is known as the oddball paradigm (Reinvang, 1998).Distractor techniquesDistractibility is assessed by the extent to which performancedeteriorates in the presence of task-irrelevant stimuli. Data fromthe distraction paradigm provide evidence that familiar stimuliare easier to ignore than novel and unexcepted ones (Pashler,1998). One of the questions that a distractor technique can helpaddress is the rate at which information held in short-termmemory decays during distraction. The Peterson and Petersontechnique (1959, cit. in Hannay, 1986) has been widely employedto investigate the effects of interference on decay in short-termmemory. The procedure consists of presenting material for retention(word triad), engaging the subject in a distractor task(e.g., counting backwards) and testing recall of the material. Thisprocedure has the advantage of extensive studies in the literatureconcerning the effects of task variables and findings inKorsakoff patients. Studies of the Korsakoff syndrome that employedthis task disclosed a steeper decay function for word triadsin amnestic patients than in normal controls or alchoholicswithout amnesic disorder (Butters&Cermak, 1980; Cermak,1982, cit. in Hannay, 1986). The technique has also been used inresearch aimed at testing the Baddeley model of working memory(Baddeley and Lewis, 1981, cit. in Eysenck, 1995)Stroop paradigmThis paradigm was first presented by Stroop in 1935 (Eysenck,1995). In the original task, participants were presented with asheet of color words printed in conflicting colors (word“GREEN” printed in red ink) and asked to name the colors inwhich the words were printed. Reaction times were measuredand compared to various control conditions in which there wasno conflict between the stimulus presented and the task to beperformed (“XXXXX” printed in different inks, color wordsprinted in black). The reaction times in the conflicting situationproved to be significantly longer while participants also made alarger number of errors than in control conditions. The task hassince been generaly adopted as a measure of the participant’sability to respond selectively to conflicting stimuli and manyvariations of the original task were developed.20

Cognitive neuroscienceDual task paradigmAnother method of testing the existence of two independentprocessing modules or subsystems is the dual task experimentalparadigm. One can argue that if two processing tasks can beperformed simultaneously without affecting each other’s performance,then the tasks must be subserved by two independentprocessing modules that can work in parallel. If the simultaneousperformance of the tasks result in interference, one can concludethat the tasks require a use of at least one shared resourceor processing component and are not independent. Dual taskparadigm was used extensively in testing the Paivio (1986##)dual coding theory.PrimingEmpirical evidence show that previous processing of a stimuluscan lead to either faster and/or more accurate or slower and/orless accurate processing of the following stimulus. The firststimulus in such case is called a prime and the effect is calledpositive or negative priming. Primes can be of very varied types.Phonological priming occurs when a target word is easier to pronouncedue to phonological similarity with the prime. In semanticpriming, the effect is due to semantic relatedness of primeand targer stimuli.Priming has been extensively used in the study of attentionalprocessing and mechanisms, semantic memory, languageprocessing, implicit cognition and elsewhere. One of the mostwidely used forms of priming tasks is the lexical decision taskin which the subject have to decide wether the taget set of characters,preceded by a priming stimulus of choice, represent aproper word or a nonword.Cognitive neuropsychologyThe goal of cognitive neuropsychology is to use existing theoriesof normal human cognition in explaining cognitive dysfunctionsfollowing brain damage. At the same time, it provides crucialdata for testing those same theories, as well as new ideasand constrains for their development. While cognitive neuropsychologybuilds in large degree on presented experimental methods,it also employs a number of distinct research approaches,methods and tools.Qualitative analysis of behaviourIn qualitative approaches to neuropsychological analysis the focusof analysis is not on the quantification of data gathered withneuropsychological test battery but on the pattern of observedbehavior and strategies used in producing it. One is not as muchconcerned with whether problem is solved as with the way inwhich it is solved. The approach calls for a careful qualitativeanalysis of the patient’s activity, of the difficulties experienced,and of the mistakes made. Developed by Luria (Luria, 1966) itstresses the importance of qualitative analysis both at the levelof behavioral observation and at the level of clinical inference.Neuropsychological test batteriesA comprehensive neuropsychological test battery is ideally aprocedure that assess all of the major functional areas generallyaffected by structural brain damage and describe its performancein a quantitive way. As Goldstein (1984) points out, it shouldbe viewed as a screening instrument that screens functional areassuch as memory, language, or visual-spatial skills for theeffect of brain damage. Besides tests that asses impairments ofspecific functions, comprehensive neuropsychological test batteriesshould also contain tests that are generally insensitive tobrain dsyfunction and provide a baseline against which the extentof impairment associated with acquired brain damage canbe measured.A number of generally available comprehensive standard testbatteries for adults exist. A review of the literature (Hodges, 1994;Groth-Marnat, 2000; Lezak, 1995; Nietzel, Bernestein, Milich,1998) indicates that most frequently used are The Halstead-Reitan and Luria- Nebraska test batteries, each having its ownadvantages and disadvantages.Flexible assessment approachIn the flexible approach, knowledge of the syndrome and thebrain-behaviour relationships is the principal factor in determiningthe selection of tools. Test selection should be germane tothe questions asked or hypotheses proposed. An encyclopaedicsource of test data and wisdom is to be found in Lezak (1995).Group and single-case studiesTwo general approaches to research in cognitive neuropsychologycan be recognized: group study and single-case study. Groupstudy is the dominant approach in traditional neuropsychology,in which the performance on one or more tasks of a group ofpatients of a given type is contrasted either with the performanceof another group of patients of a different type or with agroup of “normal” control subjects. Group studies do providedata on the average or typical deficits and range of deficits to beexpected from the groups under study, as well as data on thefrequency with which certain symptoms cluster together in patients,but there are also some important drawbacks in their usefor the study of underlying mental structure. A set of patientsclassified as Broca’s aphasics, for example, can be extremelyheterogeneous with respect to the location and extent of theirlesions, or with respect to the components of the system implicated.As only average scores for each group are known, muchvaluable information is lost in the averaging procedure and theconclusions reached may be true for only a few of the patients inthe group. Definitive statements about the effects of particularlesions or uniequivocal test of particular models of brain functioncan thus not be obtained by means of group studies (Hannay,1986).Single-case study approach stands somewhat in contrast totraditional neuropsychology. Advocates of the single-case approachstress that because brain damage may disrupt cognitivesystems in a variety of different ways, individual differencescannot be ignored. In other words, it is not possible to be surethat any two patients will manifest the same sort of cognitiveimpairment even after similar naturally occuring lesions. Whilea reasonable compromise is to carry out a case series, the strengthof the single case approach lies in its potential to reveal theoreticallyinteresting dissociations between tasks within subjects thatmight appear superficially similar in a group study. Significantdissociations between symtpoms have often been discovered inpatients whome traditional neuropsychology has grouped togetheras representative of the same syndrome category (Ellisand Young, 1996).An adequate theory of cognition should be as applicable tothe individual case as to groups of individuals. Based on properlycontrolled experimental paradigms, appropriate methods of21

Information society 2001statistical analysis, and carefully matched control groups, single-casestudies can provide a perfectly satisfactory test of cognitivetheories. When applied to rare disorders, which do notnormally occur in clinical populations, important advances inour understanding of human brain function can be made.There are also caveats to the use of single-case study. Asselective impairment found in a particular task in some patientcould just reflect his/her idiosyncratic strategy, a premorbid gapin that patient, or the way a reorganized system but not the originalnormal system operates, one must be careful at drawing theoreticalconclusions about mental structure based on single-casestudies (Shallice, 1988).It seems that further developments in the field are dependenton modification of both approaches. Group studies couldbenefit from stricter criteria for subject inclusion and the use ofmore stringent statistical procedures could reduce the inclusionof atypical group members. Proponents of the single-case approachwould achieve greater support if they were to take somesteps towards dealing with the issue of replication. The establishmentof symptoms and their explanation may become facilitatedif it can be shown that deficits occur in a number of patients.Association, dissociation and double dissociationAnother important tool in cognitive neuropsychology are thepatterns of association and dissociation between observed deficits.Association of function is indicated when different patientsexhibit impaired performance on the same set of tasks. If suchassociation across task is shown, it is tempting to assume thereis a common cognitive process or mechanism underlying performanceon all of the tasks showing impairment. However, onemust be careful as the tasks may require different cognitive processes,but these processes may be very close together anatomically,so that damage to one cognitive process is usually accompaniedby damage to all of the others.Dissociation of function occurs when two types of informationprocessing can be distinguished (Mccarthy and Warrington,1990). One aspect of performance is impaired whereas othersare preserved, which implies the existence of separate cognitivesubsystems or modules responsible for different cognitive operations.There are two types of dissociations that can be made:simple and double.A simple dissociation occurs when a patient’s performanceis normal in one task or set of tasks and poor on another set oftasks. The problem with simple dissociation is that it may notnecessarily address the discontinuity between intact and impairedfunctions; for example, a patient might do well on one task andpoorly on another simply because the other task is more difficult.Double dissociation occurs when we find a patient that showsnormal performance on task Y and is impaired on task X, andanother patient that is impaired on task Y but normal on task X.In this instance, dissociation can not be attributed to task difficulty;it is more likely that is occurred as a result of damage todiscrete functional modules. In double dissociation it is not necessaryfor patients to exhibit impaired performances on one taskand normal performances on other task; it is sufficient for performancelevels to form an interaction, regardless of whetherthere may exist significant main effects between tasks or individuals.This reciprocal pattern – the double dissociation – often providesthe strongest evidence for a degree of independence orseparability of function. Double dissociation has played an importantrole in providing evidence for the existence of separateshort-term and long-term memory stores. Whereas some patientshave impaired short-term memory but intact long-term memory,the so-called amnesic patients have severely deficient long-termmemory but intact short-term memory. These findings suggestthat there are two distinct memory systems which can sufferdamage separately.ConclusionEven though providing just a brief overview of some of the researchmethods used in cognitive psychology, the aim of thepaper was to demonstrate the width of research possibilities theyprovide, as well as to provide a glimpse into complexities thatany student of cognition is faced with. There are no words toemphasise enough the importance of sound theoretical backgroundin planning and carrying out any research in cognition,especially in view of ever more popular and advanced neurophysiologicaltechniques like functional brain imaging. In Stuss’words: “Imaging without good psychology is useless. It doesn’ttell you anything. There has been a level of explosion here, butwhat we know about the brain is still piecemeal” (cit. in TheGlobe and Mail, 2000). 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