They later applied the same testing to complex cells, but used the Y cell (subunit) model instead. This model stated that each subunits could respond differently, but the converted responses would be offset in time, so it would sum to a constant value.
The researchers initially tested simple cells and then applied the same testing method to complex cells using the Y cell (subunit) model. The model suggested that individual subunits might react uniquely but their combined responses would ultimately sum to a consistent value over time.