You've just reached 5,000 followers on Twitter. Congratulations. Now you have 5,000 people listening to you, right? Wrong! Let's take a closer look at about how many people you might be reaching with each message.
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Information is processed hierarchically, following the six steps of McGuire's Information Processing Paradigm. The tweet must first be presented to the core audience, they must be attentive to it, understand what is presented, and yield to the statement; they must retain that information and then choose to act upon it at that point. To break it down into basic steps:

1. Attention- Once a message is presented, the recipient must pay attention to it in order for it to produce attitude change.

2. Comprehension - position recommended by the communicator must be comprehended.

3. Acceptance - must yield to the message content if any attitude change is to be detectable.

4. Retention - If change is to persist, must retain changed attitude over time.

5. Action - recipient must behave on the basis of the current or changed attitude.

The important point here is that the process is hierarchical, involving compounding probabilities. This means each step in processing information is dependent upon the successful completion of the previous step, and the percentage of the target audience positively responding at each step is multiplied over the six steps.

For example:
If 60% of the Twitter audience is exposed to a message and 45% pay attention, that means only 27% of the target audience is even available for comprehension; and so on through the last step - acting upon the message.
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Once exposed to the tweet, the tweet must be processed, and successful processing involves:

  • Attention
  • Learning
  • Acceptance
  • Emotion

Conscious attention is required in order to fully process the tweet. One may not necessarily be aware of the tweet at first, but neurologically it must activate conscious processing in working memory, which will then lead to activity.


Conclusion

This full assessment is assuming they are following the general stream. This does not include segmentation features that such tools as TweetDeck provides that allows people to group certain people together and only follow their messaging. I believe Twitter really needs to work on it's social, search, and segmentation features to keep people feeling like they are being listened to and not feel like they are being drowned out by a large pool of noise.