41-60 of 97 Results  for:

  • Cognitive Psychology/Neuroscience x
Clear all



G. Campbell Teskey

The kindling phenomenon is a form of sensitization where, with repetition, epileptiform discharges become progressively longer and behavioral seizures eventually appear and then become more severe. The classic or exogenous kindling technique involves the repeated application of a convulsant stimulus. This technique also lowers seizure thresholds, the minimum intensity of a stimulus required to evoke an electrographic seizure, a process known as epileptogenesis. Endogenous kindling typically occurs following a brain-damaging event which lowers seizure thresholds to the point where self-generated epileptiform discharges recur, lengthen, propagate, and drive progressively more severe behavioral seizures. While exogenous kindling results in alterations in neuronal molecular, cellular/synaptic, and network function that give rise to altered behavior, there is a paucity of evidence for loss of neurons. In contrast, brain-damaging events, with neuronal loss, typically give rise to endogenous kindling. Kindling is a pan-species phenomenon and all mammals that have been examined, including humans, manifest exogenous kindling when seizure-genic (forebrain) structures have been targeted. Since humans display both exogenous and endogenous kindling phenomena this serves as a sober warning to clinicians to prevent seizures. Kindling serves as a robust and reliable model for epileptogenesis, focal as well as secondarily generalized seizures, and certain epileptic disorders.


Language Acquisition  

Erica H. Wojcik, Irene de la Cruz-Pavía, and Janet F. Werker

Language is a structured form of communication that is unique to humans. Within the first few years of life, typically developing children can understand and produce full sentences in their native language or languages. For centuries, philosophers, psychologists, and linguists have debated how we acquire language with such ease and speed. Central to this debate has been whether the learning process is driven by innate capacities or information in the environment. In the field of psychology, researchers have moved beyond this dichotomy to examine how perceptual and cognitive biases may guide input-driven learning and how these biases may change with experience. There is evidence that this integration permeates the learning and development of all aspects of language—from sounds (phonology), to the meanings of words (lexical-semantics), to the forms of words and the structure of sentences (morphosyntax). For example, in the area of phonology, newborns’ bias to attend to speech over other signals facilitates early learning of the prosodic and phonemic properties of their native language(s). In the area of lexical-semantics, infants’ bias to attend to novelty aids in mapping new words to their referents. In morphosyntax, infants’ sensitivity to vowels, repetition, and phrase edges guides statistical learning. In each of these areas, too, new biases come into play throughout development, as infants gain more knowledge about their native language(s).


Language and Cognitive Aging  

Lori E. James and Sara Anne Goring

The questions of whether and why language processes change in healthy aging require complicated answers. Although comprehension appears to be more stable across adulthood than does production, there is evidence for age-related changes and also for constancy within both input and output components of language. Further, these changes can be considered at various levels of the language hierarchy, such as sensory input, words, sentences, and discourse. As concluded in several other comprehensive reviews, older adults’ language production ability declines much more noticeably than does their comprehension, presumably because comprehension is able to benefit from contextual processing in a way that production cannot. Specifically, lexical and orthographic retrieval become more difficult during normal aging, and these changes appear to represent the most noticeable age-related declines in language production. Some theories of age-related decline focus on global deterioration of cognitive function, whereas other theories predict changes in specific processes related to language function. Both types of theories have received empirical support as applied to language performance, although additional theoretical development is still needed to capture the patterns of effects. Further, in order to truly understand how cognitive aging impacts the ability to understand and produce language, it is necessary to examine how age-related shifts in goals, expertise, and compensatory strategies influence language processes. There are important implications of research on language and cognitive aging, in that language can play a role in physical health and psychological well-being. In summary, our review of the existing literature on language and cognitive aging supports previous claims that language ability is asymmetrically impacted by age, with smaller overall effects of aging on comprehension than production processes.


Life Space in Older Adults  

Markus Wettstein, Hans-Werner Wahl, and Michael Schwenk

When referring to life space, researchers usually mean the area in which individuals move in their everyday lives. Life space can be measured based on different approaches, by means of self-reports (i.e., questionnaires or diaries) or by more recent approaches of technology-based objective assessment (e.g., via Global Positioning System [GPS] devices or smartphones). Life space is an important indicator of older adults’ out-of-home mobility and is meaningfully associated with autonomy, well-being, and quality of life. Substantial relationships between life space and socio-demographic indicators, health, and cognitive abilities have been reported in previous research. Future research on life space in old age will benefit from a more comprehensive and stronger interdisciplinary perspective, from taking into account different time scales (i.e., short- and long-term variability), and from considering life space as a multidimensional measure that can be best assessed based on multi-method approaches with multiple indicators.


Longitudinal, Cross-Sectional, and Sequential Designs in Lifespan Developmental Psychology  

Susan Krauss Whitbourne

Research methods in lifespan development include single-factor designs that either follow a single cohort of individuals over time or compare age groups at a single time point. The two basic types of studies involving the manipulation of the single factors of age, cohort, and time of measurement are longitudinal and cross-sectional. Each of these has advantages and disadvantages, but both are characterized by limitations because they cannot definitively separate the joint influences of age, cohort, and type of measurement. The third group of designs involves manipulation of two or more levels of each factor to permit inferences to be drawn that separate personal from social aging. The theoretical problems involved in both the single-factor and sequential designs combine with practical issues to present lifespan developmental researchers with a number of choices in approaching the variables of interest. The theoretical problems include the inevitable linking of personal with social aging, particularly evident in single-factor designs, and the fact that selective attrition leads to the differential availability of increasingly select older samples. Practical problems include the need to assign participants to appropriate age intervals and such clerical issues as the need to track participants in follow-up investigations. Researchers must also be aware of methodological issues related to task equivalence across individuals of different ages and the need to covary for potential confounds that could lead to differences across groups of participants due to such factors as education and health status. The increasing recognition of the need to address these issues is leading to a body of literature that reflects the growing sophistication of the field along with the more widespread availability of sophisticated analytic methods. As these improvements continue to raise the level of scholarship in the field, there will be a greater understanding of both ontogenetic change as well as the influence of context on development from childhood through later life.


Memory Rehabilitation in Healthy Aging  

Nicole D. Anderson

Healthy aging is accompanied by decrements in episodic memory and working memory. Significant efforts have therefore been made to augment episodic and working memory in healthy older adults. Two principal approaches toward memory rehabilitation adults are restorative approaches and compensatory approaches. Restorative approaches aim to repair the affected memory processes by repeated, adaptive practice (i.e., the trained task becomes more difficult as participants improve), and have focused on recollection training, associative memory training, object-location memory training, and working memory training. The majority of these restorative approaches have been proved to be efficacious, that is, participants improve on the trained task, and there is considerable evidence for maintenance of training effects weeks or months after the intervention is discontinued. Transfer of restorative training approaches has been more elusive and appears limited to other tasks relying on the same domains or processes. Compensatory approaches to memory strive to bypass the impairment by teaching people mnemonic and lifestyle strategies to bolster memory performance. Specific mnemonic strategy training approaches as well as multimodal compensatory approaches that combine strategy training with counseling about other factors that affect memory (e.g., memory self-efficacy, relaxation, exercise, and cognitive and social engagement) have demonstrated that older adults can learn new mnemonics and implement them to the benefit of memory performance, and can adjust their views and expectations about their memory to better cope with the changes that occur during healthy aging. Future work should focus on identifying the personal characteristics that predict who will benefit from training and on developing objective measures of the impact of memory rehabilitation on older adults’ everyday functioning.


Mental Rotation and Visual Imagery  

Fred W. Mast and Lilla M. Gurtner

Mental rotation is the ability to mentally represent the hypothetical view of an object rotated away from its actual viewpoint. It can be experimentally tested by a paradigm in which participants judge whether two stimuli are identical or not. The two stimuli are rotated and the size of angle between the two determines how long participants will take to come to a decision. This suggests that mental rotation is a mental process analogous to real rotation. This finding has been of importance for mental imagery research more broadly because (a) it illustrated that, unlike in behavioristic thinking, it is possible to research mental processes in a scientific way, and (b) because it was the foundation of many experiments supporting the similarities between mental imagery and perception, both in terms of brain activation and in terms of computational models.


Metamemory and Cognitive Aging  

Christopher Hertzog and Taylor Curley

Metamemory is defined as cognitions about memory and related processes. Related terms in the literature include metacognition, self-evaluation, memory self-efficacy, executive function, self-regulation, cognitive control, and strategic behavior. Metamemory is a multidimensional construct that includes knowledge about how memory works, beliefs about memory (including beliefs about one’s own memory such as memory self-efficacy), monitoring of memory and related processes and products, and metacognitive control, in which adaptive changes in processing approaches and strategies may be contemplated if monitoring of memory processes (encoding, retention, retrieval) indicates that alternative strategies may be required. Older adults generally believe that their memory has declined and that, on average, they have less control over memory and lower memory self-efficacy than young and middle-aged adults. Many but not all aspects of online memory monitoring are well preserved in old age, such as the ability to discriminate between information that has been learned versus not learned. A major exception concerns confidence judgments concerning whether recognition memory decisions are correct; older adults are more prone to high-confidence memory errors, believing they are recognizing something they have not encountered previously. The evidence regarding metacognitive control is more mixed, with some hints that older adults do not use monitoring to adjust control behaviors (e.g., devoting more time and effort to studying items they believe have not yet been well-learned). However, any age deficits in self-regulation based on memory monitoring or adaptive strategy use can probably be addressed through instructions, practice, or training. In general, older adults seem capable of exerting metacognitive control in memory studies, although they may not necessarily do so without explicit support or prompting.


Mirror Neurons, Empathy, and the Other  

Marco Iacoboni

Empathy is the ability to understand and share the feelings of other people. It extends also to the ability to understand and share the feelings of animals and fictional characters. Empathy is essential to properly function in social interactions. It is also typically higher for people who belong to one’s own social group and lower for people who belong to a different social group. Lack of empathy is associated with severe mental health conditions including psychopathy, narcissism, and antisocial personality disorder. Empathy is a complex, flexible, adaptive, and nuanced function for navigating social settings that involves the interplay of multiple neural systems. A crucial neural system for empathy is the mirror neuron system, formed by cells with a variety of properties and the shared feature of being activated during the actions of the self and the perception of actions of other people. The mirroring of the actions of other people in one’s brain allows an understanding from within of the other’s intentions, motivation, and feelings.


Motor Development: Biological Aspects of Brain and Behavior  

Audrey van der Meer and F. R. (Ruud) van der Weel

Developmental psychology has a long history of linking motor development to enhancement in perceptual and cognitive abilities. Because of the haphazard appearance of the very first movements, the human infant is often thought to be born with an immature brain. However, behavioral and brain research shows that infants have advanced brains that are ready to learn even before birth. The infant brain doubles in both size and weight during the first year of life. During infancy, nerve cells increase dramatically in number, they become more specialized, and up to a thousand new connections per second are formed between them. The foundation for the brain’s infrastructure is formed during the first thousand days of life. Different neural networks are formed in response to the quantity and quality of experiences a child is exposed to. In addition, the growing brain is open and moldable, it can adapt to the changing conditions surrounding it, and the brains of infants and small children show the most plasticity. Developmental neuroscience research suggests that as soon as babies start crawling at around 9 months of age, they undergo remarkable development of prospective control and timing skills at both the brain and behavioral levels when dealing with visual motion. Only a few weeks after crawling onset, infants process visual motion faster and more efficiently, and they differentiate between motion speeds and directions. Stimulating the development of motor skills that allow babies to start exploring their surroundings by themselves earlier is therefore likely to facilitate brain development.


Multistable Perception  

Alexander Pastukhov

Multistable perception is produced by stimuli that are consistent with two or more different comparably likely perceptual interpretations. After the initial perception is resolved in favor of one of the interpretations, continued viewing leads to fluctuating subjective experience, as perception spontaneously switches between alternative states. Multistable perception occurs for different modalities, including visual, auditory, tactile, olfactory perception and proprioception, and various conflicting sensory representations, such as eye dominance, depth, motion, or meaning. Despite large differences, multistable stimuli produce quantitatively similar perceptual experience with stereotypical distribution of durations of dominance phases, similar dependence on the absolute and relative strength of competing perceptual interpretations, prior perceptual history, presentation method, attention, and volitional control, and so on. Taken together, this shows that multistable perception reflects the action of general canonical perceptual mechanisms whose purpose is to resolve the conflicting evidence and ensure a single dominant perception that can be used for action. Thus, it informs us about mechanisms of perceptual decision making, including the importance of feedback mechanisms in resolving perceptual ambiguity and the role of parietal and frontal regions in facilitating changes in perception. Multistable perception provides useful constraints for models, inspiring a plethora of models of perception that combine neurally plausible mechanisms, such as neural adaptation and inhibition, or are based on the idea of predictive coding. The sensitive nature of multistable perception makes a valuable experimental tool that can reveal even minor differences due to low- or high-level influences, including genetic or clinical cases. As such, it is an important tool in studying neural and behavioral correlates of consciousness as it dissociates perception from the stimulus.


Music Perception  

Marcus T. Pearce

Music perception covers all aspects of psychological and neural processing invoked while listening to music. In order to make sense of a musical stimulus, the perceptual system must infer an internal representation of the structure present in a piece of music, including the attributes of individual events (including pitch, timbre, loudness, and timing), groups of events (such as chords, voices, and phrases), and structural relationships between such groups, so that larger-scale aspects of musical form and thematic structure can be perceived. Such representations are stored in memory at timescales ranging from seconds for echoic memory to decades in the case of long-term memory for music, which consists of schematic knowledge of musical styles, veridical memory for particular familiar pieces of music, and episodic memory for music heard at a particular place and time. Stored representations of music allow the generation of top-down expectations for the attributes of forthcoming events while listening to music, which play a role in the perception of music as it unfolds dynamically in time and also the emotional and aesthetic experience of music. Music is a communicative medium conveying affective meaning from the composer and performer to the listener, via several psychological mechanisms and using a range of cues in the music, some of which are universal, others culture-specific. Individuals show behavioral and physiological effects of listening to music from birth onward and learn the syntactic structure of the musical styles to which they are exposed within their culture, shaping their music perception. Some individuals undertake explicit musical training, which can additionally shape their perception of music, sometimes in fundamental ways. Listening to music can impair performance on concurrent tasks involving working memory due to competing access for resources but can improve performance when listening takes place prior to the task due to its positive effect on affective state. Music is a universal human cultural phenomenon whose complexity requires the activation of a diverse range of perceptual and cognitive mechanisms, making it an interesting target for psychological and neuroscientific investigation.


Neurocognitive Aging and Brain Signal Complexity  

Anthony Randal McIntosh

Brain organization can be measured across multiple spatial and temporal scales where each scale affects the other in the emergent functions that are known as cognition. As a complex adaptive system, the interplay of these scales in the brain represents the information that ultimately supports what one thinks and does. The dynamics of these multiscale operations can be quantified with measures of complexity, which are sensitive to the balance between information that is coded in local cell populations and that is captured in the network interactions between populations. This local versus global balance has its foundation in the structural connectivity of the brain, which is then realized through the dynamics of cell populations and their ensuing interactions with other populations. Considering brain function and cognition in this way enables a different perspective on the changes in cognitive function in aging. Changes in brain signal complexity from childhood to adulthood were assessed in two independent studies. Both showed that maturation is accompanied by an overall increase in signal complexity, which also correlated with more stable and accurate cognitive performance. There was some suggestion that the maximal change occurs in medial posterior cortical areas, which have been considered “network hubs” of the brain. In extending to the study of healthy aging, a scale-dependent change in brain complexity was observed across three independent studies. Healthy aging brings a shift in local and global balance, where more information is coded in local dynamics and less in global interactions. This balance is associated with better cognitive performance and, interestingly, in a more active lifestyle. It also seems that the lack of this shift in local and global balance is predictive of worse cognitive performance and potentially predictive of additional decline indicative of dementia.


Neurocognitive Aging and Functional Connectivity Using Functional Magnetic Resonance Imaging  

Hana Burianová

Determining the mechanisms that underlie neurocognitive aging, such as compensation or dedifferentiation, and facilitating the development of effective strategies for cognitive improvement is essential due to the steadily rising aging population. One approach to study the characteristics of healthy aging comprises the assessment of functional connectivity, delineating markers of age-related neurocognitive plasticity. Functional connectivity paradigms characterize complex one-to-many (or many-to-many) structure–function relations, as higher-level cognitive processes are mediated by the interaction among a number of functionally related neural areas rather than localized to discrete brain regions. Task-related or resting-state interregional correlations of brain activity have been used as reliable indices of functional connectivity, delineating age-related alterations in a number of large-scale brain networks, which subserve attention, working memory, episodic retrieval, and task-switching. Together with behavioral and regional activation studies, connectivity studies and modeling approaches have contributed to our understanding of the mechanisms of age-related reorganization of distributed functional networks; specifically, reduced neural specificity (dedifferentiation) and associated impairment in inhibitory control and compensatory neural recruitment.



Chelsea Ekstrand

The growing field of neuroimaging has offered exciting insights into the inner workings of the human brain in health and disease. Structural neuroimaging techniques provide detailed information about the physical properties and anatomy of the brain and nervous system, including cerebrospinal fluid, blood vessels, and different types of tissue. The most commonly used structural neuroimaging techniques are computed tomography (CT) and structural magnetic resonance imaging (MRI). CT uses X-rays to create a two-dimensional representation of neural tissue, whereas MRI quantifies differences in tissue density by manipulating molecules using magnetic fields, magnetic field gradients, and radio waves. Functional neuroimaging techniques provide a measure of when and where activity is occurring in the brain by quantifying underlying physiological processes. Functional neuroimaging techniques fall into two broad categories: measures of direct brain activity, including electroencephalography (EEG) and magnetoencephalography (MEG), and measures of indirect brain activity, such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and functional near-infrared spectroscopy (fNIRS). Different functional neuroimaging techniques can be used to examine different physiological changes, including electrical activity, magnetic field changes, metabolic and neurotransmitter activity, and indirect measures of blood flow to offer insight into cognitive processing. Structural and functional neuroimaging have made a profound impact on understanding the brain both during normal functioning and in clinical pathology. Overall, neuroimaging is a powerful tool for both research and clinical practice and offers a noninvasive window into the central nervous system of humans in both health and disease.


Neuropsychological Rehabilitation for People with Non-Progressive Brain Damage  

Barbara A. Wilson

Neuropsychological rehabilitation (NR) is concerned with the amelioration of deficits caused by insult to the brain. It adopts a goal-planning approach and addresses real-life difficulties. Neuropsychology studies how the brain affects behavior, emotion, and cognition. Rehabilitation is a process whereby people who are disabled work together with professional staff, relatives, and others to achieve optimum physical, psychological, and vocational well-being. Rehabilitation is not synonymous with recovery, nor is it treatment. It is a two-way interactive process with professional staff and others who aim to remediate or alleviate difficulties, adopting a holistic approach in which cognition, emotion, and psychosocial problems are treated together, aided by an increasing use of technological aids. NR enables people with disabilities to achieve their optimum level of well-being, reduce problems in everyday life, and help them return to the most appropriate environments. There may also be some partial or limited recovery of function and certainly some substitution of function. Accepting that return of normal functioning is highly unlikely, rehabilitation finds ways to help people learn more efficiently, compensate for their difficulties, and, when necessary, modify the environment. While theoretical models have proved helpful, indeed essential, in identifying cognitive strengths and weaknesses, in explaining phenomena, and in making predictions about behavior, they are insufficient, on their own, to seriously influence rehabilitation aimed at making lives more adaptable to problems encountered in everyday living. NR should focus on goals relevant to a person’s individual everyday life, it should be implemented in the environment where the person lives, and have personally meaningful themes, activities, settings, and interactions. We know from numerous studies that NR can be clinically effective. Although rehabilitation can be expensive in the short term, there is evidence that it is cost-effective in the long term.


Numerical Cognition  

Aviv Avitan and Avishai Henik

Quantities, amounts, and numbers are dealt with on a regular basis. Their manipulation is necessary for making countless decisions. Research in the area of numerical cognition seeks to delineate how numerical information is represented, manipulated, and utilized. In parallel, research in this area traces the phylogenetic and ontogenetic trajectories of numerical abilities. A comprehensive understanding of numerical cognition and its brain basis has important implications for various disciplines. These disciplines include education, neuroscience, and economics. Furthermore, understating numerical cognition will help to foster good mathematical skills and support those who struggle with numerical and mathematical concepts.


Object Perception  

Scott P. Johnson

Visual scenes tend to be very complex: a multitude of overlapping surfaces varying in shape, color, texture, and depth relative to the observer. Yet most observers effortlessly perceive that the visual environment is composed of distinct objects, laid out across space, each with a particular shape that can be inferred from partial views and incomplete information. Moreover, observers generally expect objects to be continuous across space and time, to have a certain shape, and to be solid in three-dimensional (3D) space. The cortical visual system processes information for objects first by coding visual features, then by linking features into units, and last by interpretation of units as objects that may be recognizable or otherwise relevant to the observer. This way of conceptualizing object perception maps roughly onto processes of lower-, middle-, and higher-level visual processing that have long formed the basis for investigations of visual perception in adults, as well as theories of object perception, the ways visual deprivation reduces object perception skills, and the developmental time course of object perception in infancy.


The Origin of Psychology in the Humanities  

Sven Hroar Klempe

The term “psychology” was applied for the first time in the 16th century. Yet the most interesting examples appeared in three different contexts. The Croatian poet and humanist Marko Marulić (ca. 1520), the German philosopher and Calvinist Johann Thomas Freig (1575), and the German Lutheran philosopher Rudolph Goclenius (1590). Marulić’s manuscript is likely lost, and neither of the other two defined the term. Even the interests of the three went apparently in different directions. Marulić focused on poetry and history, Freig on physica, and Goclenius on theological issues. Nevertheless, they had something in common, and this may represent the gate through which the ways they conceived the term can be understood. They all dealt with the soul, but also that it was a highly disputable concept and not uniformly understood. Another commonality was the avoidance or reinterpretation of Aristotle’s philosophy. The Florentines’ cultivation of Plato had influenced Marulić. Freig was a Ramist, thus, also a humanist who approached philosophical questions rhetorically. Goclenius belonged partly to the same movement. Consequently, they all shared a common interest in texts and language. This is just one, yet quite important aspect of the origin of psychology as a science. Thus, these text- and humanity-oriented aspects of psychology are traceable from the very beginning. This reaches a peak point when Alexander Baumgarten publishes his two volumes on aesthetics, as they were based on Christian Wolff’s Psychologia empirica (1732). They are also traceable in Kant’s critical phase, and even more in Wundt’s folkpsychology. Thus there is a more or less continuous line from the very first uses of the term psychology and some tendencies in social and cultural psychology. In other words, psychology is pursued along an historical line that ends up in the German, and not the British enlightenment.


Pavlovian and Instrumental Conditioning  

Federico Sanabria

Conditioning is the change in the response to a stimulus either because of the relation of that stimulus to other stimuli (Pavlovian conditioning), or because of the relation between the response and other stimuli (instrumental conditioning). These relations are formulated in terms of differences in conditional probability known as contingencies. Pavlovian contingencies refer to the difference in the conditional probability of one stimulus (the outcome, or O) given the presence vs. the absence of another stimulus (the conditioned stimulus, or CS). A conditioned response (CR) may be strengthened by a positive Pavlovian contingency (excitatory conditioning) or it may be weakened by a negative Pavlovian contingency (inhibitory conditioning). CRs are anticipatory or modified responses to the O, so their topography depends on the nature of the O (appetitive vs. aversive); the proximity between and congruency of O and CS; prior experience with the CS, O, and their contingency; the magnitude of their contingency; and the characteristics of other stimuli in the environment. Instrumental contingencies refer to the relation between one stimulus (the discriminative stimulus, or SD), a response (or operant, R), and the outcome of that response (O). The nature of the O and of its contingency with the R determines whether the O strengthens or weakens the R: Os that introduce an appetitive stimulus (positive reinforcement) or remove an aversive stimulus (negative reinforcement) strengthen the R. Positive reinforcement is typically arranged on a subset of one or more Rs following a set of rules known as a schedule of reinforcement. The probability that an R is reinforced may depend on the number of Rs (ratio schedules) or the amount of time (interval schedules) since the last reinforcer. The topography and strength of instrumental Rs depend on variables that are analogous to those that affect Pavlovian CRs: the amount and nature of prior experience with the O; the proximity, congruency, and contingency of R and O; and characteristics of other stimuli in past and present environments. Contemporary quantitative models of Pavlovian and instrumental conditioning recognize the importance of contextual stimuli that compete for cognitive and behavioral resources, constraining and shaping the expression of target responses. These models have guided the bulk of recent empirical research and conceptual developments, leading to a progressively unified view of learning and motivation processes. Along the way, Pavlovian and instrumental research have demonstrated their utility in addressing a broad range of consequential societal problems.