Example: I see something moving, there's contact. Then there's an unpleasant feeling and perception recognize it as a spider. Mental formations on how to deal with the "threat" of a spider arises.
A new consciousness is born. Does it contain the mental formation that caused it to arise?
Thank you
Good question. The way it was explained to me, the twelve nidanas are all "made" from each other, they are all made from the same "stuff". It's like when there is water, the wave on the water and the foam on top of the wave - they all "grow" from one another. Similarly, consciousness is "made from" mental formations and feelings/perceptions "grow from" consciousness like foam on top of the wave.
So when the "new" consciousness is "born" - yes, it certainly "contains" (rides on top of, made of) the mental formations that led to it. Which is one of the ways karma perpetuates itself.
Mental formations (aka "tendencies") define the overall shape of the future action in broad brushstrokes, and then consciousness, feelings, perceptions, craving, etc. get more and more specific until the action itself, which leads to some results, that manifest as new experience on the next cycle and so on - this is how "tendencies" perpetuate themselves.
Tendencies (formations), consciousness, attraction/aversion, and karma grow from each other and carry the impulse of each other, so Samsara keeps rolling forward like this.
If consciousness arises from mental formation...
Actually consciousness doesn't arise from mental formation. Mental formation "conditions" the arising of consciousness, but that doesn't mean it gives birth to consciousness. Consciousness together with its mental factors (feeling, perception, volition) have been compared to a king and his retinue. They always appear together. From Comprehensive Manual of Abhidhamma:
The cetasikas are mental phenomena that occur in immediate conjunction with citta or consciousness, and assist citta by performing more specific tasks in the total act of cognition. The mental factors cannot arise without citta, nor can citta arise completely segregated from the mental factors. But thought the two are functionally interdependent, citta is regarded as primary because the mental factors assist int he cognition of the object depending upon citta, which is the principal cognitive element. The relationship between citta and the cetasikas is compared to that between a king and his retinue. Although one says "the king is coming" the king does not come alone, but he always comes accompanied by his attendants. Similarly, whenever a citta arises, it never arises alone but always accompanied by its retinue of cetasikas.
Eye contact is caused by the union on eye+light+eye consciousness. So the consciousness is already there to begin with. It's not something that arises later.
Consciousness is of six kinds:
Feelings, perception, mental formations and consciousness arise together. Not one after the other. Think of it as drinking chocolate milk. What do you taste first? Is it the chocolate? Is it the milk? Is it the sugar? Or do you taste them altogether? In this analogy, think of the consciousness as the water in chocolate milk. Water has no taste unless there is something mixed in it. In the same way consciousness is neutral and simply the bare awareness of the experience.
