Inhibition of Return (IOR) is a difficulty in processing stimuli presented at recently attended locations. IOR is widely believed to facilitate foraging of a visual scene by decreasing the probability that gaze will return to previously fixated locations. However, there is a lack of clear evidence in support of the foraging facilitator hypothesis during scene search. The original R. M. Klein and W. J. MacInnes' (1999) Where's Waldo study reported a forward bias in the distribution of fixations that was taken as evidence for the foraging facilitator hypothesis. The present study was designed to replicate R. M. Klein and W. J. MacInnes' (1999) but include detailed analysis of fixation distributions in order to test the precise predictions of the foraging facilitator hypothesis. The results indicate that latencies of saccades returning to 1-back (and possibly 2-back) locations during visual search are elevated. However, there is no evidence that the probability of returning to these locations is significantly less than control locations. Eye movement behavior during search of visual scenes does not support the view that IOR facilitates foraging.

*temporal*effect may facilitate visual search by “

*repelling attention*” away from previously attended locations to help observers avoid reinspecting them (pg. 346; Klein & MacInnes, 1999). This would result in a decrease in the probability of returning the eyes to a location once it has been fixated (Klein & Hilchey, in press; Wang & Klein, 2010). If IOR can be shown to have such a

*spatial*consequence it can be said to

*facilitate foraging*(Klein, 1988; Klein & MacInnes, 1999).

*SD*= 1.06) and 3.87° (

*SD*= 0.89), respectively with no difference across probe locations. Only saccades landing within 1.5° of the six target locations were used in the analysis, ensuring that hits for each probe location did not overlap. The distance to probes that were immediately fixated was significantly shorter (mean = 3.28,

*SD*= 1.02) than to probes that were missed (mean = 4.52,

*SD*= 1.55,

*F*(1, 31) = 82.97,

*MSE*= 101.3,

*p*< 0.001), with no effect of whether the probe was 1- or 2-back or probe location. The difference between hits and misses was probably due to decreasing visibility of the probe with increasing eccentricity. Saccadic latencies to the probes were averaged across 60°/300° and 120°/240° to investigate whether there was a linear effect of angular deviation. Given that the probe always appeared about 40 ms into a critical fixation, the duration of the critical fixation (fixation duration) was used as a proxy for saccadic latency. Mean fixation durations are displayed in Figure 2.

*F*(3, 96) = 3.426,

*MSE*= 1652,

*p*< 0.05, a main effect of Back,

*F*(1, 32) = 4.178,

*MSE*= 5898,

*p*< 0.05, but no interaction,

*F*< 1. Across both Back conditions, saccades to probes at previous fixation locations (0°) were preceded by significantly longer fixations (mean = 273 ms,

*SD*= 63.6) than saccades to probes at 120°/240° (mean = 246 ms,

*SD*= 51.6,

*p*< 0.05), and 180° (mean = 246 ms,

*SD*= 43.4,

*p*< 0.01). The difference between 0° and 180° suggests an IOR effect of 27ms. Saccades to probes at 60°/300° (mean = 259 ms,

*SD*= 52.3) were also preceded by significantly longer fixations than saccades to probes at 180° (

*p*< 0.05). There were no other significant differences. The pattern of fixation durations across probe locations cannot be accounted for by variation in the eccentricity of the probes given that the mean eccentricity of the probes did not vary across probe locations. These results confirm the linear relationship between angular deviation and preceding fixation duration observed in previous studies (Klein & MacInnes, 1999; MacInnes & Klein, 2003; Smith & Henderson, 2009a, under review).

*F*(3, 48) = 86.76,

*MSE*= 0.001,

*p*< 0.001) and penultimate fixation location (

*F*(3, 48) = 13.28,

*MSE*= 0.001,

*p*< 0.001). However, what is unclear from this analysis is whether this distribution of saccades is due to inhibition of regressive saccades or facilitation of forward saccades. Closer examination of the saccade probabilities revealed that regressive saccades occurred significantly less than forward saccades (1-back: difference = 0.11,

*p*< .001; 2-back: difference = 0.05,

*p*< 0.01) but significantly more than saccades directed 60°/300° away (1-back: difference = 0.06,

*p*< 0.001; 2-back: difference = 0.017,

*p*< 0.05). This increased frequency of regressive saccades compared to directions other than forward would not be expected if the forward bias was caused by IOR, and is more consistent with a tendency for the eyes to move forward (

*saccadic momentum*, Smith & Henderson, 2009a) rather than a tendency for them not to move backward. However, the coarseness of this analysis presented here and in previous studies (Klein & MacInnes, 1999; MacInnes & Klein, 2003) does not allow the precise predictions of the foraging facilitator hypothesis to be tested. More precise analysis of the spatial distribution of fixations is required to determine the influence of spatially specific oculomotor IOR on fixation probability at the specific location of previous fixations.

*saccadic momentum*(Smith & Henderson, 2009a). If IOR has a spatial effect on subsequent saccade programs it should be evident as a spatially specific decrease in the probability of fixations landing at prior fixation locations, not just an overall forward bias. The distribution of saccades presented in Figure 3 may hide this spatially specific effect due to averaging across saccades of all amplitudes in a particular direction.

*F*(3, 48) = 5.507,

*MSE*= 0.001,

*p*< 0.01) and 2-back fixation locations (

*F*(3, 48) = 7.294,

*MSE*= 0.001,

*p*< 0.001). However, the main effect of Location was not due to a lower probability of return fixations, but rather a greater probability of fixating 180° away from previous locations. The probability of returning to the 1-back location (mean = 0.086,

*SD*= 0.03) was not significantly different from the 60°/300° (mean = 0.082,

*SD*= 0.02) or 120°/240° locations (mean = 0.089,

*SD*= 0.03). The only location with a significantly greater fixation probability was 180° (mean = 0.113,

*SD*= 0.03; difference = 0.027), which was greater than all other locations (all

*p*s < 0.05). A similar bias to fixate the 180° location seems to account for the main effect of Location relative to 2-back. The probability of returning to the 2-back (mean = 0.053,

*SD*= 0.016) and 60°/300° locations (mean = 0.054,

*SD*= 0.016) were both significantly less than the 120°/240° (mean = 0.069,

*SD*= 0.021,

*p*s < 0.05) and 180° locations (mean = 0.081,

*SD*= 0.033,

*p*s < 0.01), with no significant difference between them.

*SD*= 0.03) was significantly greater than the probability of fixating the same location when order effects were eliminated (mean = 0.042,

*SD*= 0.009, difference = 0.044,

*p*< 0.001; see Figure 5, Shuffled-squares). The probability of fixating the 2-back location (mean = 0.053,

*SD*= 0.016), while lower than 1-back location, was also significantly greater than the shuffled control (mean = 0.040,

*SD*= 0.01, difference = 0.013,

*p*< 0.01; see Figure 5, Shuffled-diamonds). As can be seen from Figure 5, the probability of fixating the shuffled control was significantly greater than chance (the probability of landing within 1.5° of a randomly selected location on the screen; mean = 0.013,

*SD*= 0.005,

*p*< 0.001), confirming that only a limited number of screen locations are fixated during search and this cycling through limited locations is captured by the shuffled baseline.