1981 Paper

Dr Luthersand has been investigating the effects of brain lesions upon visual discrimination in the octopus. For his most recent experiment he procured two groups of 12 octopuses. Group E, the experimental group was bought from "Podiprods", a commercial breeder of laboratory cephalopods; they were all two-year-old females and had not taken part in any experiment before. Because of the soaring cost of marine molluscs, Dr Luthersand made up his control group, Group C, with octopuses which he bad bought previously. These too were all females and matched Group E in both age and weight; they had been used in one previous experiment a year earlier, but only in another control group.

Dr Luthersand is interested in the role of the vertical lobe of the octopus brain in pattern discrimination. Therefore, he lesioned the vertical lobe in each of the members of Group E. After the operation one octopus died and another looked decidedly ill. These two animals took no further part in the experiment. To keep the size of the two groups the same, two members of the control group were eliminated at random.

After the operation on Group E all 20 animals were pretrained on a simple left-right discrimination to familiarise them with the apparatus. Half the animals were rewarded for choosing the left panel in the test chamber, the other half were rewarded for choosing the right panel. After this pretraining both groups were trained to discriminate wide stripes from narrow stripes. Group E was rewarded for choosing the panel with wide stripes. Group C was rewarded for choosing the panel with narrow stripes. Dr Luthersand decided that each animal had learnt the discrimination when it had successfully chosen the rewarded pattern three times in a row.

All animals were then tested on a second discrimination between vertical and horizontal stripes. Group E was rewarded for choosing the horizontal stripes, Group C for choosing the vertical stripes. Again a criterion of three correct responses in a row was applied.

The results of these two experiments are given in Table 1.

TABLE 1. Mean number of trials to criterion.

GROUP E GROUP C
NARROW VS. WIDE 27.1 16.4
VERTICAL VS. HORIZONTAL 10.3 8.1

Dr Luthersand now performed a two-way split-plot Analysis of Variance with the following results:

TABLE 2. Results of ANOVA.

Main effect of stimulus type F(1,18) = 10.356 p < 0.05
Main effect of group F(1,18) = 4.931 p < 0.05
Interaction F(1,18) = 8.471 p < 0.05

From these results he concluded:

  1. that vertical/horizontal discrimination is easier for octopuses than wide/narrow
  2. that lesions of the vertical lobe affect narrow/wide discrimination but not vertical/horizontal discrimination; therefore, the neurones responsible for encoding the size of patterns must lie in the vertical lobe.

[Back to Criticise-the-Experiment List] [Back to Main Page]