His wide-ranging areas of scholarship and expertise included clinical assessment, psychoanalysis, cognitive schemas, mental representation, psychopathology, depression, schizophrenia, and the therapeutic process, as well as the history of art.
In 1954, Blatt entered the PhD program in Personality Development and Psychopathology in the Department of Psychology at the University of Chicago under the supervision of Morris I. Stein.
During his postdoctoral fellowship at the University of Illinois Medical School and at Michael Reese Hospital's Psychiatric and Psychosomatic Institute he was influenced by two psychologists, Mary Engel and Sarah Kennedy Polka, who had been trained at the Menninger Foundation in Topeka, Kansas, and introduced Blatt to Rapaport's approach to diagnostic psychological testing.
Concurrently, he embarked on psychoanalytic training at the Western New England Institute for Psychoanalysis (WNEIP), supported by a grant from the Foundations Fund for Research in Psychiatry.
This contact with Schafer enabled Blatt to consolidate his interest in Rapaport's work, especially the links between cognitive processes and personality organization and between representational development and psychopathology.
During his 51 years at Yale, 48 years as chief psychologist, Blatt was the teacher and mentor of many students and colleagues who then went on to develop distinguished careers of their own (in alphabetical order): John Auerbach, Beatrice Beebe, Rachel Blass, Ted Brodkin, Diana Diamond, Kenneth Levy, Howard Lerner, Suniya Luthar, Patrick Luyten, Thomas Odgen, Donald Quinlan, Barry Ritzler, Golan Shahar, Paul Wachtel, Steven Wein, and many distinguished others.
His collaboration initially with Donald Quinlan at Yale and later with David Zuroff, then at Quinnipiac College in Hamden, Connecticut, and now at McGill University in Montreal, Quebec, Canada, paved new grounds in the research and treatment of depression.
In addition to directing and participating in pre and post doctoral clinical training for psychologists in the department of psychiatry, Blatt, for many years, offered a core seminar on personality development and psychopathology in the graduate clinical psychology training program in the department of psychology and supervised research of graduate and undergraduates, most notably the senior essay of David C. Cohen, “Characteristics of complex problem solving following the induction of success or failure”, that won the Angell Award in 1964 as the outstanding senior essay and the 1996 doctoral dissertation by Carrie Schaffer, “The role of attachment in the experience and regulation of affect” that was accepted with distinction, a rare honor at Yale, especially for a dissertation in the clinical area.
Blatt and colleagues subsequently realized that the two depressive experiences, anaclitic (or dependent) and introjective (or self-critical), could be linked to two fundamental developmental pathways, relatedness and self-definition, that occur in both normality and psychopathology and that mature or develop in complex interaction with each other.
[4][5][6][7] Blatt proposed that not just psychopathology but indeed normal psychological development and functioning could be understood as reflective of these fundamental developmental lines, relational and self-definitional.
For example, two aspects of self- definition, self-criticism and efficacy, were found to affect academic achievement among mid-school students,[12] maternal self-criticism and dependency were found to affect mother-child communication [13] and self-criticism was found to affect goal construction in young adulthood [14] Integrating concepts from cognitive developmental psychology (i.e., ideas from Jean Piaget and Heinz Werner), psychoanalytic developmental theory (i.e., ideas from Beatrice Beebe, Anna Freud, Edith Jacobson, Margaret Mahler, and Daniel Stern) and attachment theory and research (i.e., ideas from Mary Ainsworth, John Bowlby, and Mary Main), Blatt [15][16] proposed a model of personality development focusing on the development of cognitive-affective schemas of self and others, schemas that in the psychoanalytic literature are termed object relations, internalizations of relationships with emotionally significant others or objects.
This stage, assumed to take place in the early months of life, results in the formation of boundary constancy, the awareness of a distinction between self and other, between self and nonself.
The third achievement, evocative or object constancy, begins in the second year of life and is coincident with a concrete-perceptual stage, in which thinking is dominated by perceptual features and resemblances.
The capacity for higher levels of intersubjectivity—that is, the ability to understand others’ psychological, rather than just physical, perspectives—also emerges here, in consequence, this stage is associated with identity formation and the beginnings of adult intimate relationships.
At this stage, the ability to integrate complexities and conflicts is not yet fully consolidated, however, so the individual remains vulnerable, usually to excessive but more focused depressive states, in response to relational loss if anaclitic or to achievement failures or moral transgressions if introjective.
And finally, in late adolescence and early adulthood, individuals begin to develop conceptual schemas, in which one integrates all previous representational levels into complex, coherent understandings of self and significant others that take into account conflicts and contradictions in a person's character.
Spontaneously descriptions of self and significant others (i.e., parents, therapist or close friend) are scored for Conceptual Level (CL, with sensorimotor, concrete-perceptual, external and internal iconic, and conceptual levels, per the above developmental sequence), which is considered a structural variable reflecting degree of psychological organization of significant-figure descriptions,[24][25] as well as for three content factors (Benevolent, Punitive and Striving).
They noted that Piaget's formulations of the child's development of the capacity to represent space and time provided a theoretical structure for understanding the development of the representation of space and time in art, as well as in science in the history of Western Civilization [39][40] Blatt and Ritzler [41] established a continuum of thought disorder on the Rorschach based on the degree of boundary disturbance, with a collapse of self-other and self-nonself boundaries (contaminations) at the lowest level, intrusion of intense emotion into realistic perception (confabulations) at middle levels, and arbitrary unrealistic relationships based on spatiotemporal contiguity of independent objects (fabulized combinations) at the highest level of impaired boundary representation.
Much later, Blatt, Besser, and Ford [42] found that therapeutic gain in anaclitic and introjective inpatients was expressed in changes in different types of thought disorder.
Shahar, Blatt and Ford [50] also found that "mixed-type" inpatients (anaclitic-introjective), compared to the "pure" type patients, though initially more symptomatic, were more likely to improve in long-term, psychodynamically oriented psychotherapy.
Sidney Blatt's extensive theoretical and research contributions have articulated continuities between variations in adaptive personality development with various forms of maladaptive personality development (psychopathology), thereby providing a theoretically coherent, empirically validated alternative to the dominant, but extensively criticized (e.g.,[55]) Diagnostic Statistical Manual of Mental Disorders (the DSM) categorical, symptom-based, disease model of psychopathology (e.g.,[11][56]).
Blatt and colleagues have demonstrated that these representations or cognitive-affective interpersonal schemas are the basis foundations of various forms of adaptive and maladaptive personality organization and are also central in the treatment process and to sustained therapeutic change.