Table 1.
Top: Summary of measures of choice behaviour, planned contrasts assessed by t-test. Bottom: Blood results.
| Phase | Measure | Feedback | Placebo | Depletion | p | Cohen’s d |
|---|---|---|---|---|---|---|
| Acquisition | Correct responses | 38.63 (3.2) | 39.27 (1.82) | .34 | .25 | |
| Trials to criterion | 10.59 (6.76) | 9.83 (4.63) | .61 | .13 | ||
| Win–stay | Veracious | .97 (.07) | .98 (.04) | .326 | .18 | |
| Lose–shift | Spurious | .06 (.16) | .03 (.1) | .478 | .22 | |
| Reversal | Correct responses | 33.44 (4.7) | 34.13 (4.06) | .536 | .16 | |
| Trials to criterion | 16.63 (8.57) | 15.23 (7.6) | .502 | .17 | ||
| Win–Stay | Veracious | .93 (.13) | .96 (.1) | .331 | .26 | |
| Lose–Shift | Spurious | .11 (.19) | .12 (.17) | .889 | .06 | |
| Perseveration, immediate | 3.69 (2.1) | 3.97 (2.0) | .594 | .137 | ||
| Perseveration, phase | 3.81 (3.68) | 3.67 (3.0) | .865 | .042 | ||
| Blood | TRP:LNAA (1) | .11 (.02) | .10 (.02) | .239 | .50 | |
| TRP:LNAA (2) | .11 (.03) | .005 (.004) | 4.96 × 10 –20 | 4.9 | ||
| Valine (1) | 225 (45.10) | 230 (46.56) | .662 | .11 | ||
| Valine (2) | 841.30 (238.69) | 820.86 (218.96) | .733 | .09 | ||
| Methionine (1) | 29.60 (4.98) | 27.62 (6.44) | .191 | .34 | ||
| Methionine (2) | 67.70 (23.97) | 63.07 (20.71) | .431 | .21 | ||
| Isoleucine (1) | 64.60 (17.47) | 66.14 (17.66) | .738 | .09 | ||
| Isoleucine (2) | 218.13 (92.84) | 218.34 (129.83) | .994 | .002 | ||
| Leucine (1) | 128.23 (27.82) | 126.76 (30.26) | .846 | .05 | ||
| Leucine (2) | 344.37 (134.99) | 342.90 (137.30) | .967 | .01 | ||
| Tyrosine (1) | 67.27 (12.50) | 66.45 (18.53) | .843 | .05 | ||
| Tyrosine (2) | 170.40 (41.242) | 196.55 (82.14) | .132 | .40 | ||
| Phenylalanine (1) | 59.33 (8.53) | 58.93 (9.54) | .865 | .04 | ||
| Phenylalanine (2) | 111.07 (43.94) | 120.07 (63.98) | .530 | .16 | ||
| Tryptophan (1) | 61.97 (9.63) | 59.21 (9.80) | .280 | .28 | ||
| Tryptophan (2) | 201.53 (77.05) | 7.83 (5.33) | 2.68 × 10 –14 | 3.55 |
Note: (1) signifies baseline values; (2) denotes results from sample taken after approximately 4.5 h. TRP:LNAA is the ratio between tryptophan and all large neutral amino acids (listed in table), thought to be most reflective of brain serotonin (Hood et al., 2005). Emboldened values indicate statistical significance at p < .05.