EXPERIMENT 2.b

Experiment 2.b was a reading task using the exact same stimuli as in Experiment 2.a. If similar results are observed in the reading task, then we can infer that the results obtained in Experiment 2.a are not due to the cognitive load created by the extra adjectives or the visual complexity of the images.

Method Participants

Twenty six French speaking undergraduate students from the University of Geneva took part in the experiment. This time, all of them had participated in the picture naming task. They received course credit for their participation. All had normal or corrected-to-normal vision.

Material

We used the exact same stimuli as in Experiment 2.a in a reading task. The sequences were shown in Arial Narrow 16.

Procedure

Stimulus presentation was controlled by the DMDX software (Forster & Forster, 2003). The stimuli appeared on a computer screen and participants were instructed to read them aloud as quickly and as accurately as possible. Before the presentation of each stimulus, a fixation cross stayed on the screen for 500 ms followed. The stimulus appeared 200 ms after and remained on the screen for 800 ms. A blank screen would then follow and stay for 500 ms.

The experiment lasted about fifteen minutes with three breaks included. Within each block the trials were pseudo-randomized to maximize distance between similar stimuli. Naming latencies of the noun phrases were measured by means of a voice key. Reaction times were measured starting from the onset of the stimulus to the beginning of the naming response. The experiment started with a training session with two stimuli.

Results

Voice key failures were checked and corrected with speech analyser software. Errors, no responses, technical errors were discarded from the analysis and reaction times above 1037 and below 271 ms were withdrawn from the data analysis. A total of 2.5% of the data was therefore removed (2.1% of errors and 0.4 % outliers). Spoken latencies data were fitted with

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linear regression mixed models (Baayen et al., 2008) with the software (project, R-development core team 2005; Bates & Sarkar, 2007). Error rates were fitted with logit mixed-effects models (Jaeger, 2008) with same random- and fixed-mixed-effects factors. We controlled by-participants and by-items random adjustments to intercepts. Results can be observed in Table 7. As for Experiment 2.a, the model was done in two steps.

First we analyzed the NP condition.

Mean reaction times are 488 ms for N, 532 for A+N, 567 for N+A. The NP condition was first analyzed: N is 44 ms shorter than A+N being the shortest 2W condition. The main effect of condition is confirmed: (F(1, 2840) = 67.48 p<.0001). Contrasts across conditions were analysed. Again, spoken latencies for the N condition are faster than all the other conditions (N vs. A+N: t(2840) = -6.56 p<.0001; N-N+A: t(2840) = -11.52, p<.0001. Naming latencies for the A+N condition are 35 ms faster than the N+A condition (A+N vs. N+A: t(2840) = -6.09 p<.0001).

Error rate showe no difference between N and A+N (z<1), but a difference between N and N+A (z= -2.15, p<0.031) and a difference between A+N and N+A (z=-2.83, p<.004).

Table 7

Mean Naming Latencies for the Three Conditions of Noun Phrases (ms).

Mean (SD) Error (%)

Order effect Difference (ms)

N 488 (86) 0,03% N-A+N 44

A+N 532 (99) 0,36% N-N+A 79

N+A 567 (110) 1,62% A+N-N+A 35

Note: numbers in brackets are Standard Deviation for each average

As for Experiment 2.a, we included the two 2W conditions (order condition) together with the following fixed effect variables linked to those conditions: the frequency of the sequence, the length of the adjective, the frequency of the adjective. The frequency of the sequence was log transformed. All these variables were included in a backward-stepwise regression analysis.

The variables for which the coefficient did not reach significance (with a p value inferior to 0.05) were discarded from the original model in a step-by-step fashion. The final model

77 Chapter 3: Encoding of simple noun-phrases versus adjective-noun phrases included only the variables for which the coefficient reached significance. The frequency of the sequence and the frequency of the adjective were removed from the final model²¹. Results of the remaining significant coefficients are reported in Table 8 while the overview of the fixed effect can be seen in Figure 9 (with A, The order condition; B, The length of the adjective).

Table 8

Regression Coefficients (β) with the t and p Values for Each of the Fixed Effect Predictors in the Regression Analyses of Experiment 2.b.

Predictors Β Std. Error

t t(2051) p(MCMC)

(Intercept) 6,29E+03 3,14E+01 200.53 .0000

Order 6,02E+01 1,01E+01 5.93 .0000

Length of the adjective -3,75E+01 9,98E+00 -3.76 .0002 Frequency of the adjective -7,86E-02 6,06E-02 -1.30 .194

Figure 9. Overview of the effects of the fixed effect variables for experiment 2.b with A, the mean reaction times for each order condition and B, the mean reaction times for the length (short and long) condition .

DISCUSSION

Experiment 2.b was run as a control experiment of Experiment 2.a to test whether the order effect might be due to a heavy visual-cognitive load. Four major results are observed.

21 The values of the frequency of the adjective are reported are they are above >1 for t.

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NP condition

First, we replicate the order effect in the NP condition with shorter RTs for the single N condition and shorter RTs for the A+N condition relative to the N+A condition. The fact that we observe shorter naming latencies for N relative to the two 2W conditions suggest that encoding of one word in a reading task is less costly than encoding of two words. This might be due to the presentation of two items (words) versus one item in which case the longer reaction times for the 2W condition simply comes from the fact that the system has to deal with more visual information. However, the fact that this effect is replicated in the picture naming task where both 1W and 2W conditions are elicited by only one picture suggest that results from Exp. 2.b might simply mean that encoding of NPs in a reading task extends beyond the initial word.

Order condition

Then we observe an effect of order with shorter naming latencies for the A+N condition relative to the N+A condition. The fact that the order effect between A+N and N+A is still observed in a reading task suggests that the order effect reported in Experiment 2.a is not due to visual processes.

Frequency of the sequence

As for experiment 2.a, the frequency of the sequence did not affect reading times.

Frequency of the adjectives

We do not report a frequency effect of the adjectives in the reading which suggests that the frequency effect reported in the naming task might be an artifact due to the material. Taken together, the inhibitory effect of the frequency of the adjectives in Experiment 2.a (naming) and the non-significant in Experiment 2.b (reading) seem to suggest that the number of adjectives selected in Experiment 2 was too low. Experiment 3 will investigate whether the repetition of the eight adjectives might account for this result.

Length effect

As for the naming task in Experiment 2.a, we replicate an effect of the length of the adjective.

The fact that it is consistent across the two experiments in our study suggests along with other parallel results that similar phonological processes are involved during naming a picture and

79 Chapter 3: Encoding of simple noun-phrases versus adjective-noun phrases reading a word (as proposed by Roelofs, 2004). However, we need to mention that some studies comparing picture naming and reading tasks in the literature reported an effect of length for reading only but not naming (Bates et al., 2001).

Concerns with the design of Experiment 2.a and b.

Experiment 1 and 2 presented an order effect for which several issues were raised but also ruled out. However, the design of these experiments still presents a weakness as the nouns and adjectives are not entirely balanced. In all these experiments, more nouns than adjectives were used. The adjectives were therefore repeated more often than the nouns. As the A+N condition starts with an adjective, the shorter naming latencies for this condition might be explained by the fact that adjectives were used more frequently within the task. Moreover, the position of the adjectives in N+A sequences was not always entirely appropriate. The following experiment will therefore examine these two issues. Experiment 3 will use the exact same nouns and adjectives in different syntactic orders and will investigate whether the preferred position of the adjective might explain the order effect obtained in the previous experiments.