Visual deficits in schizophrenic patients are of particular interest because they reflect the deficient circuits of information processing in the brain. In our previous work, we showed that schizophrenic patients have decreased peak amplitudes and reduced cortical activity when performing a vernier offset discrimination task. However, it remains unclear whether these reduced amplitudes are caused by diminished activity or larger variability of amplitude peak latencies. Here, we analyzed the patients’ deficits in terms of intra-participant trial-by-trial variability. ERPs variability were estimated using a two-step graph-based method. We found that patients had larger N1 peak amplitude latency variability than matched controls. After correcting for the latency variability, the patients still showed smaller and more variable N1 peak amplitudes than controls. Hence, peak amplitudes are both diminished and highly variable in the patients. These observations provide empirical evidence in support of theories of increased noise in patients with schizophrenia.