The role of recommendation algorithms in online user confinement is at the heart of a fast-growing literature. Recent empirical studies generally suggest that filter bubbles may principally be observed in the case of explicit recommendation based on user-declared preferences rather than implicit recommendation based on user activity. We focus on YouTube which has become a major online content provider but where confinement has until now been little-studied in a systematic manner. We aim to contribute to the above literature by showing whether recommendation on YouTube exhibits phenomena typical of filter bubbles, tending to lower the diversity of consumed content.
Video camera tubes were devices based on the cathode ray tube that were used in television cameras to capture television images prior to the introduction of charge-coupled device CCD image sensors in the s. In these tubes, the cathode ray was scanned across an image of the scene to be broadcast. The resultant current was dependent on the brightness of the image on the target. The size of the striking ray was tiny compared to the size of the target, allowing horizontal scan lines per image in the NTSC format, lines in PAL ,  and as many as lines in HiVision. Any vacuum tube which operates using a focused beam of electrons, originally called cathode rays , is known as a cathode ray tube CRT. These are usually seen as display devices as used in older i.