Namaste Jaydeen,
As you probably know, there are many, many books on Yoga available. What aspects of psychology are you interested in? Perhaps we can help you find something with a bit more specific information.
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Namaste,
Shishya
ॐ
ॐ सह नावतु । सह तौ भुनक्तु । सह वीर्यं करवावहै । तेजस्वि नावधीतमस्तु मा विद्विषावहै ॥
"Together may we be protected. Together may we be profited. Together may we do a hero's work. May we learn intelligently. May we never hate one another."
-Brihadaranyaka & Taittiriya Upanishads