Thanks for the question and for introducing the terms rational and emotional. I could geek out all day talking about this kind of stuff. The principles I cover in my book, as well as the principles I subscribe to in all situations, are firmly rooted in what’s called dual process type of theories. That is, there are multiple processes or factors involved in behavior. I don’t think people are all rational or all emotional in most situations. From a behavior economics perspective, being rational means you make the best decision based on the information you have available. I discuss that in-depth in chapter 3 of Design for the Mind. This isn’t true. People make a lot of irrational decisions on a regular basis. Any decision where you lose more money, time, or another resource than you gain is irrational. Yet people stay in jobs that pay them less than they are worth, they stay in relationships where they have stopped getting value out of the time they spend, they continue working on projects that are losing money for their company, etc. That isn’t rational. On the other hand, people don’t make decisions or engaged in long-term behaviors based solely on emotion. At some point you receive either negative or positive feedback on your behavior, and then the more rational part of your brain contributes to the decision to continue engaging in that behavior. I cover all of the types of things in chapters 2 through 4 and again in chapter 8 in Design for the Mind. People do tend to rely more on emotion or what’s referred to as heuristics when they have to make quick decisions, over more rational processes if they have time or the behavior is considered a planned behavior.
As far as your other questions - I’m familiar with research suggesting attention spans are getting shorter. I’m not able to locate the actual research article, but here is a link to an article about the article: here
Much of the research done on attention focuses on children and adults with ADD/ADHD. While I don’t think having a short attention span is inherently a bad thing, it becomes problematic when we are diagnosing people with conditions like ADD or ADHD if the trend is moving towards a shorter attention span.
Some mass cultural and behavioral shifts that immediately come to mind are use of mobile phones to access the internet, and use of social media platforms. Pew research has found much of the world is accessing the internet through mobile phones. Additionally, they have found that a majority of US adults belong to two or more social media platforms. This wasn’t the case a decade or so ago. I think there are a lot of design implications behind understanding how people are accessing the internet on mobile phones (perhaps not even more modern Smartphones). Also, as I discuss in Design for the Mind, we can influence our users and promote certain behaviors through their social networks.
I hope this answers your questions. I enjoyed thinking about this.