Why we are declaring same thing two time in .h file in iOS

Question

I have one confusion whenever i am seeing others code in iOS. Why we are declaring same thing two time in .h file in iOS. i have e.g. is

@interface ViewController : UIViewController<GPUImageMovieWriterDelegate,GPUImageInput>
{
GPUImageMovie *_movieFile;
GPUImageOutput<GPUImageInput> *_sketchFilter;
GPUImageMovieWriter *_movieWriter;

}
 @property (nonatomic,retain)    GPUImageMovie *movieFile; 
 @property (nonatomic,retain)    GPUImageOutput<GPUImageInput> *sketchFilter; 
 @property (nonatomic,retain)    GPUImageMovieWriter *movieWriter;
@end

Here why we are declaring two tile _movieFile ,_movieFile and movieWriter. any one knows exact reason then please explain.