Finding the edges of things

Having never taken Psychology in college I am in the midst of listening to the podcast of Yale's Intro Psych course. It is expectedly fascinating and ripe for discussion. One theme that's come up twice now is the brain's excellent ability to pick out the edges of things. To distinguish between words even when there is no measurable gap between the last phoneme of one word and the first phoneme of the next. To separate a visual perception into distinct objects amid a jumble of colors, brightnesses, and depths that any landscape presents. In both cases, the brain can be fooled by clever psychologists, visual illusions being the best known.

This gets me thinking about great acuity in finding the edges of all sorts of other things besides spoken language and visual stimuli, and about how and when that edge finding ability can be confused. What is the edge between my emotional involvement in my marriage and my spouses? Where is the edge between the set of strangers who are members of "my tribe" (think Brooklyn or Somerville, not Kikuyu or Lao) and those who are not, one to be trusted the other to be feared? How do I instantly sort the dangers of modern life the street into real and figmentary? What's the edge of reasonable caution? What's the edge between frugality and wastefulness? Finding edges seems wrapped up in sorting, about putting some concept or stimulus in one category and its neighbor in another category. I have absorbed from many a popular science article or documentary that some huge proportion of my brain is devoted to visual processing. Can I, do I, tap into that to make distinctions in other categories of thought?

Yesterday's run destination: Montana Ave.

Yesterday's menu:
breakfast: last of the granola
lunch: turkey noodle soup
dinner: Ezra's chickpeas with spinach and peppers