The category-order effect (COE) is observed when the
categorical properties of items within the first half of a given
list affect recall performance in a mixed-list serial-recall task.
The present study examines whether the advantage is due to
other sub-categorical properties (e.g., orthographic similarity
and word frequency) rather than an artifact of stimuli used in
previous studies (e.g., numbers vs. nouns). Participants were
presented with numeric stimuli and nouns from a variety of
semantic categories while their orthography and word
frequency were systematically manipulated. The results
suggest that a large portion of the COE can be attributed to
the sub-categorical properties of the items.