Much is unknown about adult attachment style formation. We investigate whether negative reinforcement schedules promote hallmark features of secure and anxious attachment styles in a shock threat support-seeking paradigm. Participants ostensibly asked for help from another participant seated in another room. Each time a shock threat signal appeared they were to press a button to indicate their need for help. The supporter could then stop the imminent shock. The reliability of the supporters was varied such that some supporters were consistent (continuous reinforcement) whereas others were inconsistent (variable ratio reinforcement). Results indicated that inconsistently responsive others, reinforcing on a variable ratio schedule, led to heightened approach-related attentional biases toward the supporter, measured by event-related potentials, increased positive attachment associations with the supporter, implicitly measured via a lexical decision task, and more negative explicit evaluations of the supporter.