I am deeply suspicious of "movements" within critical discourse of any medium or mode of communication. I tend to align myself more with a McLuhan-esque model of thinking which holds that media are extensions of ourselves and of each other.* To simply state where, when, and how one era, movement, or period ends and another begins is too simplistic and problematic. Nevertheless, this manner of thinking restructures thought to the extent that media and institutions come to embody the properties and categories through which we understand them, despite not intrinsically existing as such. In other words, I would venture to guess that even though categorizing modes of thought, media, narrative, etc. is inherently reductive, it nonetheless enables our cultural institutions and media to embody the oversimplifications that we impose on them.
In terms of the cinema's technological evolution, there are undeniably certain "movements," e.g. the introduction of sound, color, animation (though animation preceded photographic properties of cinema), and countless other subtle advances which affected the construction of images. There were also institutional, economic, and social factors that guided particular movements in cinema such as the implementation of the Hays Code in the early days of cinema or the MPAA in the late 60's. Even beyond these factors specifically relating to cinema and its production are cultural and social components that have yielded certain stages in the development of the movies as an art form, critical artifiact, and technological medium. There are probably hundreds, thousands more factors that influence periods in cinema, and this broad idea should be something that all critics, viewers, and scholars should take note of. Interestingly, many of these factors convened in the late 1960's and early 1970's, resulting in many undeniable changes in the direction of American cinema. However, in favor of highlighting these changes and asserting a liberated filmmaking atmosphere (an attitudes that persists even today) in which American cinema "came into its own" and made great strides to catch up with European art cinema, it's very tempting to screen out certain elements of the time that may call the consistency and tidiness of such an argument into question.
No one can deny that American cinema changed immensely at that time, but the reception of that (or any) change often depends on the already established context and conditions under which such change takes place. In terms of stylistic and narrational aspects of filmmaking, of which there were many shifts in the 1970's, many of these aesthetic properties were influenced by the technical knowledge and expansion of cinematic media. For example, that filmmakers began employing widescreen cameras changed how shots could be framed, which then affected how filmmakers envisioned compostions. This example is overly simple, yes, but it effectively captures the notion that many of the artistic changes were undergirded by not only subtle technical changes in technology as well as the cultural familiarity and preparedness for that change. If a culture, audience, or individual is accepting of change, they/she/he are usually already accustomed to what to expect in this change and are therefore more willing to embrace it. This is usually the case in more subtle alterations in films and filmmaking capabilities as the increased use of widescreen camera lens late 60's and 1970's American cinema shows.
However, when it comes to changes that greatly affect the technical, stylistic, narrational, and even structural aspects of cinema, cultures/audiences/individuals are almost unanimously opposted to such change. This is likely because they have built a familiarity (consciously and unconsciously) with the specific elements that contributed to cinematic storytelling before sound and therefore came to view sound in cinema as bastardization of all that cinema was. But the overriding claim I'm making -- one that deserves much more critical thought -- is that how positively or negatively a movement or change is received seems to vary according to social and technical conditions, i.e. the nature of the change is measured and understood by manners in which the "new" elements interact with existing familiar styles and cinematic elements, which are influenced by social and technical conditions. Thus, epistemological and phenomenological questions about cinema are central to responsible criticism of and thought about it.
Today, we are experiencing something similar to the introduction of sound in cinema: digital cinema. While there was no one film that signaled the onset of a new mode of cinematic intrepretation -- a la The Jazz Singer -- many movies of the past 20 years (Young Sherlock Holmes, The Abyss, Jurassic Park, Terminator 2: Judgment Day, Toy Story, the "Star Wars" prequels, Miami Vice, Inland Empire) have given ushered (in some cases, demanded) new ways of constructing and interpreting cinematic images and movements. The digital movement is happening continually, and its effects are seen in movies of all shapes and sizes, not just films using the technology. It has been met with plenty of resistance, i.e. those claiming that the only true form of cinema is that which is captured on celluloid and projected onto a screen. This perspective is baffling in how stubborn its advocates are. It also doesn't hold up under close scrutiny, but instead only works in generalities. The very discussion of whether it's "good" or "bad" for cinema is more revealing of the ideological issues that sustain particularly limited approaches to media, art forms, and organizations. Nevertheless, ideology enables us to make sense of and advance these very modes of communicating, so to try to act independently of them is foolish as well.
My argument (in very broad terms) is that we are married to forms of language and categorization, which enable the formation and understand of eras, movements, etc. We are trapped within them but inevitably constituted by them. While I am skeptical about movements, I cannot deny their very real presence and take part in the construction of said changes as well. Nevertheless, it's very important to be reflective participants rather than passive viewers of cinema (or any medium) and ask questions of such "changes" that reduce so many technological, social, and cultural factors contributing to all media to one simple plane. Maybe we should question the glory of the American 1970's, actively ponder the validity of the overwhelmining critical denouncement of digital cinema, or the basic claims that certain modes of storytelling or film styles are inherently bad or not "artistic." That is not to say that any broad assumption is incorrect; just that we should push ourselves to think about all factors that may contribute to any advances or movements of any kind. Reducing them to generalities promotes highly reductive understanding of them.
Assuming we choose to engage in critical thought about cinema that refuses to abide by a single plane of understanding, one that takes easily tagged movements and simplified understandings of periods, genres, and visual techniques with a grain of salt, what then is cinema? This is harder to answer. Nevertheless, one must acknowledge the nearly infinite amount of elements that contribute to an experience many consider to be simple: watching a movie. For those who approach cinema on a critical level, this becomes all the more important (as the digital movement reminds) as the medium itself and the other media that influence it continue to change along with our relation to them. Approaching the production and interpretation of cinema from affective, cognitive, and social schools of thought may reveal much about position to and understand of it; its narrational, representative, and structural properties as they pertain to the relation to and understanding of visuality. Doing so may finally spark the critical thought that such an influential, complex, and important medium demands.
* Note: I do not worship at the altar of McLuhan in all matters of media since I find him overly simplistic regarding some things, but I think his contributions to communication and media studies are essential and innovative in the age of electronic media.