Reproductive memory for diagonal and nondiagonal patterns in chimpanzees

Two male juvenile chimpanzees were trained to reproduce from memory geometric patterns composed of lighted cells in a 3 x 3 matrix. In Experiment I, subjects reproduced 3-cell horizontal, vertical and diagonal patterns with either 0- or 5-second delay between stimulus offset and response. Diagonals were more difficult and were more affected by delay than were nondiagonal patterns. The sequence of response to diagonals was less structured than to nondiagonals. In Experiment II, more complex 4-cell patterns were used and, following training, subjects were tested for transfer to new patterns. Again, diagonals were more difficult to reproduce than nondiagonals. Transfer of training to new patterns requiring different motoric responses was successful. Similar to Experiment I, organization of responding was greater for nondiagonals than for diagonals. These results are discussed with regard to the presence of internal representation of visual information in nonhuman primates.