Reflecting on the Conceptualization of Specific Learning Disabilities in the 21 st Century

Over the past years, learning disabilities (LD) or specific learning disabilities (SLD) have emerged as one of the most studied fields of developmental disabilities and have become synonymous with special education itself due to how frequently students are placed under this category. It is also the special education category which has brought the most disagreement among scholars, researchers, and educators to this day, given that, LD has not been established as a distinct discipline; that is until now no causal relationship has been determined between the phenomenology of LD and the factors which cause them. Despite formal definitions, a lack of understanding of their nature and their interpretation exists, which indicates that the main goal of a distinct discipline is not fulfilled yet [1,2].


Introduction
Over the past years, learning disabilities (LD) or specific learning disabilities (SLD) have emerged as one of the most studied fields of developmental disabilities and have become synonymous with special education itself due to how frequently students are placed under this category. It is also the special education category which has brought the most disagreement among scholars, researchers, and educators to this day, given that, LD has not been established as a distinct discipline; that is until now no causal relationship has been determined between the phenomenology of LD and the factors which cause them. Despite formal definitions, a lack of understanding of their nature and their interpretation exists, which indicates that the main goal of a distinct discipline is not fulfilled yet [1,2].
The main goal of conceptualizing LD is to provide effective and appropriate instruction so as to improve the characteristics of the disabilities that students demonstrate. As a field, we have advanced from simple interpretations that have focused on the phenomenology of behavior and cognitive characteristics to more intricate interpretations that encompass cognitive, neurobiological, and educational factors. However, we have yet to come to a consensus regarding the "what" and "why" of LD that constitutes them a single and distinct entity.
In the United States (US), studies on better understanding the nature of LD and determining best practices in their identification have been continuous. In 1989, the National Joint Committee on Learning Disabilities (NJCLD), based on new evidence and scientific findings, attempted to eradicate inherent ambiguities in the identification of the field, by formulating the following definition: Learning disabilities is a general term that refers to a heterogeneous group of disorders manifested by significant difficulties in the acquisition and use of listening, speaking, reading, writing, reasoning, or mathematical abilities. These disorders are intrinsic to the individual, presumed to be due to central nervous system dysfunction, and may occur across the life span. Problems in self-regulatory behaviors, social perception, and social interaction may exist with learning disabilities but do not by themselves constitute a learning disability. Although learning disabilities may occur concomitantly with other disabilities (for example, sensory impairment, intellectual disabilities, emotional disturbance), or with extrinsic influences (such as cultural or linguistic differences, insufficient or inappropriate instruction), they are not the result of those conditions or influences (NJCLD, 1989).
In 2004, the IDEA regulation maintained the same definition of SLD as previous versions of the law and regulations. Notably, an attempt to expand the identification process occurred by including both a process based on the child's response to scientific, research-based intervention, such as Response to Intervention (RTI) and the use of other alternative research-based procedures, such as the Patterns of Strengths and Weakness (PSW) model. The IDEA definition reads as follows: "Specific learning disability means a disorder in one or more of the basic psychological processes involved in understanding or in using language, spoken or written, that may manifest itself in the imperfect ability to listen, think, speak, read, write, spell, or to do mathematical calculations, including conditions such as perceptual disabilities, brain injury, minimal brain dysfunction, dyslexia, and developmental aphasia." [3] and "Specific learning disability does not include learning problems that are primarily the result of visual, hearing, or motor disabilities, of mental retardation, of emotional disturbance, or of environmental, cultural, or economic disadvantage." [3].
The IDEA definition seems to introduce a hierarchy of processes, with language being dominant, whether oral or written. Furthermore, the disorder is not connected with difficulties in academic achievement alone, but also with cognitive deficits (reasoning disorders), a trait that reflects what we nowadays call metacognitive function. No mention of central nervous system dysfunctions appears yet, but there are references to similar cases deriving from neurological disorders.
The NJCLD definition, highlights that the term "in general" is vague [4], much like the term "specific" in the Individuals with Disabilities Educational Act [3] definition, thus, allowing various interpretations.
The Diagnostic and Statistical Manual of Mental Disorders (DSM) utilizes the term specific learning disorder. Revised in 2013 [5], the current version, DSM-5, broadens the previous definition to reflect the latest scientific understanding of the condition. The most significant changes in this revised edition are regarding the need for support depending on the severity level just like in other developmental disorders [6]. Moreover, this change reflects a conceptual change in how we, as educators, think about what it means for individuals to have a disability and how they respond to it.
The main characteristics of all these attempts to define and conceptualize LD are based on the idea of "unexpected underachievement" [7] because individuals with LD do not learn to read, write and/or do arithmetic despite the absence of conditions that are correlates of low achievement, such as intellectual disability, sensory impairment, etc. These conditions are commonly referred to as exclusionary because they represent factors in which low achievement is expected. All the above characteristics are key features of the construct and include low achievement, cognitive discrepancies, and poor instructional response. We can measure all these attributes, but measurement will always be imperfect.
The term can also be conceptualized with a broad sense which means all learners with low achievement can be categorized under LD. This approach is an arbitrary process that introduces unreliability into decisions about learners who may or may not be appropriately placed under this category [8,9]. Snowling & Hulme [10] have argued that reading disabilities involving word recognition and comprehension, while correlated, they represent distinct dimensions of a broader classification. However, treatment needs are different depending on the affected component. This argument helps us understand how students with LD low achievement in may also have more than one of the domains (e.g. reading, math, writing). In other words, it is not unexpected to have learners that experience disabilities in more than one academic domain and issues related to one domain to impact the performance on others. For example, LD in reading comprehension can be correlated with issues in math problemsolving.
In conclusion, from the infancy of the field to today, the search for conceptualizing LD is based on the phenomenology that has led us to the definitions but also to the disagreements in the field. The only constant in the construct of LD is that of low achievement; however, it can be difficult to measure low achievement with reliability and validity similar to accurately measuring the intellectual quotient (IQ). Well-established psychometric challenges [11] have been reported regarding assessment and eligibility in heterogeneous groups, including students from marginalized, minoritized, and diverse backgrounds that constitute a large percentage of the student population. To move forward as a field, we are still looking for answers to the "what" and "why" of LD hoping that new research, especially in the neurocognitive domain, will advance our understanding.