Final answer:
Vertical nystagmus is most closely associated with intoxication by Phencyclidine (PCP), which acts on the NMDA glutamate receptor and can cause dissociative effects.
Step-by-step explanation:
Vertical nystagmus, a rapid involuntary movement of the eyes, is most closely associated with intoxication by Phencyclidine (PCP). This substance acts as an antagonist of the NMDA glutamate receptor, which differs from the action of other hallucinogens such as LSD and mescaline that are serotonin agonists. Among the options provided, PCP is known to cause dissociative effects and can lead to symptoms like vertical nystagmus that are typically not associated with the use of serotonergic hallucinogens such as LSD, DMT, MDMA, or mescaline