Table 3.

Intercorrelations among progressive ratio variables

Parameter	Reinforcers	Session Duration	Breakpoint	Total Responses	Mean Reinforced IRI	Mean Nonreinforced IRI
Latency	−0.79***	−0.59**	−0.67**	−0.57**	0.71***	0.23
Reinforcers		0.84***	0.97***	0.92***	−0.76***	−0.34
Session Duration			0.89***	0.89***	−0.53**	−0.25
Breakpoint				0.99***	−0.68***	−0.34
Total Responses					−0.61**	−0.32

IRI, the duration of inter-response intervals following reinforced (“reinforced IRI”) or nonreinforced (“nonreinforced IRI”) responses. Results were calculated from data obtained during the first progressive ratio session of week 5 from male Wistar rats with a history of diet alternation (n = 15; Chow A/I / Preferred) or control Chow A/I conditions (n = 14).

^**P < 0.01, and

^***P < 0.001 vs. 0.