Final answer:
The bank teller's oversight can be attributed to inattentional blindness, a well-documented phenomenon where the focus on one element can cause a person to miss others in plain sight.
Step-by-step explanation:
The bank teller's experience described in the scenario is an example of inattentional blindness. This term refers to the psychological phenomenon where an individual fails to perceive an unexpected stimulus that is in plain sight, simply because their attention is focused on another task or aspect of their environment. This can occur even if the unobserved object is something as conspicuous as a person in a gorilla suit walking across a scene, as demonstrated in the famous study by Simons and Chabris. The teller was so focused on the threat of the weapon that she did not register other details such as the robber's facial features.
The famous experiment involving a gorilla suit illustrates this principle well, where participants focused on counting basketball passes did not notice the gorilla. Likewise, participants who missed a red cross among black and white moving objects in another experiment were also experiencing inattentional blindness. Thus, when our attention is selectively absorbed, we can miss details and elements that would otherwise be obvious.
The bank teller's failure to notice the bank robber's facial features is an illustration of inattentional blindness, where a person does not perceive stimuli outside the focus of their attention, despite its clear visibility.